When clicking with the right mouse-button on one of the system buttons, and then dragging the mouse over the button until leaving it, without releasing the mouse-button itself, the button stays marked. It is reproducible in all themes.

Workaround:

public Form1()
{
    InitializeComponent();
 
    this.radRibbonBar1.RibbonBarElement.RibbonCaption.MinimizeButton.MouseLeave += Button_MouseLeave;
    this.radRibbonBar1.RibbonBarElement.RibbonCaption.MaximizeButton.MouseLeave += Button_MouseLeave;
    this.radRibbonBar1.RibbonBarElement.RibbonCaption.CloseButton.MouseLeave += Button_MouseLeave;
}

private void Button_MouseLeave(object sender, EventArgs e)
{
    RadImageButtonElement btn = sender as RadImageButtonElement;
    if (btn != null)
    {
        btn.IsMouseDown = false;
    }
}

To reproduce: 
1.Add a RadForm.
2.Create a UserControl with RadRibbonBar.
3.Apply Window8 theme to the RadRibbonBar and to the RadForm.
4.Use the following code:

Me.RadRibbonBar1.CloseButton = False
Me.RadRibbonBar1.MinimizeButton = False
Me.RadRibbonBar1.MaximizeButton = False
Me.RadRibbonBar1.RibbonBarElement.Text = String.Empty

5.When you add the UserControl to the RadForm and run the application, the QuickAccessToolbar items are cut off.

Workaround:

Me.RadRibbonBar1.RibbonBarElement.QuickAccessToolBar.OverflowButtonElement.Padding = New Padding(0, 0, 0, -15)
Me.RadRibbonBar1.RibbonBarElement.QuickAccessToolBar.InnerItem.Padding = New Padding(0, 10, 0, -10)

To reproduce:
- Add a tab to a RadRibbonForm form.
- Collapse the ribbon and press the Alt key to show the KeyTips.
- Select a tab by pressing the corresponding key.
- You will notice that the tab is not expanded.

Workaround:
void radRibbonBar1_KeyTipActivating(object sender, CancelEventArgs e)
{
    keyExpanded = true;
}

void radRibbonBar1_Click(object sender, EventArgs e)
{
    keyExpanded = false;
}

bool keyExpanded = false;

void radRibbonBar1_CommandTabSelected(object sender, Telerik.WinControls.UI.CommandTabEventArgs args)
{
    if (!radRibbonBar1.Expanded && keyExpanded)
    {
        radRibbonBar1.Expanded = true;
    }
}

To reproduce:

Add a RadRibbonBar, a tab and a group. In the group add a RadButtonElement. Add two buttons on the form. One for enabling and one for disabling the RadButtonElement.  Start the application , collapse the RadRibbon and disable the button inside. Now expand it and you will see the visual bug.

Workaround:

Subscribe to the ExpandedChanged event of the RadRibbonBar and if the RadRibbonBar is expanded and the button is disabled re-enable and re-disable the button. This will correct its visual appearance. 

To reproduce:
1. Add a RadRibbonBar and add several buttons with images as follows:

public Form1()
{
    InitializeComponent();

    RibbonTab tabItem1 = new RibbonTab();
    tabItem1.Text = "Manage";
    radRibbonBar1.CommandTabs.Add(tabItem1);

    RadRibbonBarGroup radRibbonBarGroup1 = new RadRibbonBarGroup();
    radRibbonBarGroup1.Text = "radRibbonBarGroup1";
    tabItem1.Items.Add(radRibbonBarGroup1);

    RadButtonElement radButtonElement1 = new RadButtonElement();
    radButtonElement1.Image = Properties.Resources.about;
    radButtonElement1.TextImageRelation = TextImageRelation.ImageBeforeText;
    radButtonElement1.Text = "First Button";
    radRibbonBarGroup1.Items.Add(radButtonElement1);

    RadButtonElement radButtonElement2 = new RadButtonElement();
    radButtonElement2.Image = Properties.Resources.about;
    radButtonElement2.TextImageRelation = TextImageRelation.ImageBeforeText;
    radButtonElement2.Text = "Second Button";
    radRibbonBarGroup1.Items.AddRange(new RadItem[] { radButtonElement1, radButtonElement2 });

    RadRibbonBarButtonGroup radRibbonBarButtonGroup1 = new RadRibbonBarButtonGroup();
    radRibbonBarButtonGroup1.Orientation = System.Windows.Forms.Orientation.Vertical;
    radRibbonBarButtonGroup1.ShowBorder = true;

    RadButtonElement radButtonElement3 = new RadButtonElement();
    radButtonElement3.Text = "Button One";
    radButtonElement3.Image = Properties.Resources.about;
    radButtonElement3.TextImageRelation = TextImageRelation.ImageBeforeText;

    RadButtonElement radButtonElement4 = new RadButtonElement();
    radButtonElement4.Text = "Button Two";
    radButtonElement4.Image = Properties.Resources.about;
    radButtonElement4.TextImageRelation = TextImageRelation.ImageBeforeText;
  
    radRibbonBarButtonGroup1.Items.AddRange(new RadItem[] { radButtonElement3, radButtonElement4 });
    radRibbonBarGroup1.Items.Add(radRibbonBarButtonGroup1);
}

2. Run the applications, re-size the form horizontally until all buttons are collapsed to smallest size, then click the form's maximize button. As a result all buttons are drawn without text.

Workaround:
protected override void WndProc(ref Message message)
{
    const int WM_SYSCOMMAND = 0x0112;
    const int SC_MAXIMIZE = 0xF030; 

    switch (message.Msg)
    {
        case WM_SYSCOMMAND:
            int command = message.WParam.ToInt32() & 0xfff0;
            if (command == SC_MAXIMIZE) 
            {
                this.Size = new System.Drawing.Size(300, 300);
            }
            break;
    }
    base.WndProc(ref message);
}

To reproduce:
1. Add a RadRibbonBar
2. Apply Office2013Light theme
3. Use the following code snippet:

public Form1()
{
    InitializeComponent();

    this.radRibbonBar1.CloseButton = false;
    this.radRibbonBar1.MinimizeButton = false;
    this.radRibbonBar1.MaximizeButton = false;
    this.radRibbonBar1.ApplicationMenuStyle = Telerik.WinControls.UI.ApplicationMenuStyle.ApplicationMenu;
}


Workaround:
this.radRibbonBar1.RibbonBarElement.ApplicationButtonElement.Margin = new Padding(3, 8, 0, 0);

1. Create a new application with RadRibbonForm.
2. Set the ApplicationThemeName to TelerikMetro.
3. Run the application. You will see that the quick access toolbar is visible and there are not items in it.

1. Create a new RadRibbonForm and add some tabs.
2. Set the backstage view mode.
2. Run the application. The application icon will not be visible.

When you set the ApplicationMenuStyle property to  BackstageView at design time and set its  theme to Office2013Dark or Office2013Light you lose the ability to return back to the designer page  by clicking the back button.

Workaround: select  the RadRibbonBar via Visual Studio's Document Outline window (ctrl+W, U) or via Visual Studio's Property Grid's Component combobox (on the top of the property grid)

To rperoduce:
- Set the themes as follows:
var theme = new Office2010BlackTheme();
new Telerik.WinControls.RadControlSpy.RadControlSpyForm().Show();
ThemeResolutionService.ApplicationThemeName = theme.ThemeName;

this.radRibbonBar1.ElementTree.EnableApplicationThemeName = false;
this.radRibbonBar1.ThemeName = "ControlDefault";

- Start and collapse the ribbon tabs. 
- Click on a tab to show its controls.

Workaround: Use the ApplyThemeToControlTree method instead of settig the ApplicationThemeName property.
ThemeResolutionService.ApplyThemeToControlTree(this, "Windows");

To reproduce:

Add a RadRibbonBar and a RibbonTab.
Add a control to the form (for example a textbox).
Subscribe to its LostFocus event and set the tab's visibility to collapsed in the event handler.
When you start the application click the textbox, then click the tab and you will see that the tab will hide but the content will stay visible.

To reproduce:
public RadRibbonForm1()
{
    InitializeComponent();
    radRibbonBar1.Expanded = false;
}     

private void button1_Click(object sender, EventArgs e)
{
    if (ribbonTab2.Visibility == Telerik.WinControls.ElementVisibility.Visible)
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    }
    else
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Visible;
    }
}

Workaround:
private void button1_Click(object sender, EventArgs e)
{
  
    this.radRibbonBar1.RootElement.SuspendLayout();
    if (ribbonTab2.Visibility == Telerik.WinControls.ElementVisibility.Visible)
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    }
    else
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Visible;
    }
    this.radRibbonBar1.RootElement.ResumeLayout(false);          
}

To reproduce: Add a RadRibbonBar, add a ribbon tab with some groups and buttons. Run the application, autohide the content of the tabs, minimize the application, maximize it, open the tab the buttons are overlapping each other.

I have a RadGalleryElement in my RadRibbonBar.  It has both a minimum and maximum row count of four, and currently contains 6 items.  I have "selection" enabled for the Gallery.  The selection states persist for the first row of items, but do not for my second row.

To reproduce: Add a RadRibbonBar, set it to backstage view, add a ribbon tab, run the application autohide the content of the tabs, you will notice that 2 pixels are cut off the BackstageView button

To reproduce:

1. Add a RadRibbonBar with a RadDropDownListElement and some other elements.
2. Use the following code:

for (int i = 0; i < 5; i++)
{
    RadListDataItem item = new RadListDataItem();
    item.Text = "Item" + i;
    this.radDropDownListElement1.Items.Add(item);
}
this.radRibbonBar1.EnableKeyMap = true;
this.radDropDownListElement1.KeyTip = "S";         
this.radDropDownListElement1.DropDownStyle = Telerik.WinControls.RadDropDownStyle.DropDownList; 
3. Press Alt, then 2. You will see the key tips for the drop down and its sibling items. 
4. Press S. You are expected to be navigated to the RadDropDownListElement, but are not. 

Here it is illustrated the behavior: http://screencast.com/t/Qmvqufznjt

To reproduce:
1.Create a new Visual C# -> Telerik Windows Forms Application
2.Drag a RadRibbonBar control onto RadForm1
3.Create a single tab "First Tab" (otherwise you cannot collapse the ribbon)
4.Drag a button onto the form and add the following code to the click event handler:
RibbonTab tab = new RibbonTab("Test");
this.radRibbonBar1.CommandTabs.Add(tab);
tab.IsSelected = true;
5.You should end up with something like the attached png file.
6.Run the project and click the button. You should see the new tab is created and selected.
7.Close the project and run it again. This time, collapse the ribbon before clicking the button. No new tab is visible on the ribbon. Even if you click on the [First Tab] to show the full ribbon.
8.Click the expand ribbon button on the right and the new tab will then appear.

Workaround:
bool isExpanded = this.radRibbonBar1.Expanded;
this.radRibbonBar1.Expanded = true;
RibbonTab tab = new RibbonTab("Test " + this.radRibbonBar1.CommandTabs.Count); 
this.radRibbonBar1.CommandTabs.Add(tab);
tab.IsSelected = true;
this.radRibbonBar1.Expanded = isExpanded;

To reproduce:
- Set the theme and show the help button.

Workaround:
Hide the fill and the border in Visual Style builder