To reproduce: add 3 ribbon tabs at design time and use the following code snippet:

public Form1()
{
    InitializeComponent(); 
}

private void InsertTabs()
{
    for (int i = 1; i <= 5; i++)
    {
        var index = radRibbonBar1.CommandTabs.IndexOf(this.ribbonTab3);
        radRibbonBar1.CommandTabs.Insert(index, new RibbonTab(string.Format("Tab {0}", i.ToString())));
    }
}

private void Form1_Load(object sender, EventArgs e)
{
    InsertTabs();
}

Workaround: insert the tabs in the form's constructor.

To reproduce:
- Add ribbon bar to a form and set its IsMdiContainer property to true.
- Add an MDI child with a ribbon bar and minimize it.

To reproduce:

public partial class Form2 : RadRibbonForm
{
    public Form2()
    {
        InitializeComponent(); 

        this.WindowState = FormWindowState.Maximized;
        this.radRibbonBar1.ApplicationMenuStyle = ApplicationMenuStyle.BackstageView;
        this.AllowAero = false;         
        this.Icon = Properties.Resources.WinFormsIcon;     
    }
}

Workaround1: set AllowAero property to true if it is possible.
Workaround2: this.radRibbonBar1.RibbonBarElement.RibbonCaption.MouseMove += RibbonCaption_MouseMove;
private void RibbonCaption_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == System.Windows.Forms.MouseButtons.Left && this.WindowState== FormWindowState.Maximized)
    {
        this.WindowState = FormWindowState.Normal;
        this.Location = new Point(this.Location.X,e.Location.Y);
    }
}

Workaround:

public Form1()
{
    InitializeComponent();
     
    this.radRibbonBar1.KeyTipShowing+=radRibbonBar1_KeyTipShowing;
}

private void radRibbonBar1_KeyTipShowing(object sender, CancelEventArgs e)
{
    RadButtonElement b = sender as RadButtonElement;
    if (b!=null && b.Enabled==false)
    {
        e.Cancel = true;
    }
}

To reproduce:
Add RadRibbonForm and change the theme(for example to WIndows8Theme). Run the project. The system buttons are covered by the fill of RadRibbonBarElement.

Workaround:
Set the DrawFill property of RadRibbonBarElement to false.
this.RibbonBar.RibbonBarElement.DrawFill = false;

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

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

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:

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

Please refer to the attached gif file.

Workaround: close manually the popup by calling the this.radSplitButtonElement1.DropDownMenu.ClosePopup(Telerik.WinControls.UI.RadPopupCloseReason.Mouse) method.

With particular cultures the alt key is used for specific symbols and this is why the user should be able to use one of the alt key for symbols and the other one for the key tips.

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: 
1. Add a RadRibbonBar and a RadButtonElement in one of the groups.
2. Set the RadButtonElement.UseCompatibleTextRendering property is set to false.
3. Set the RadButtonElement.Enabled property to false.

You will notice that the text is hardly read compared to version Q2 2014.

Workaround: Currently, the possible solution is to set the RadButtonElement.UseDefaultDisabledPaint property to false and subscribe to the EnabledChanged event where you can modify the ForeColor in order to make it gray when the button is disabled and apply a gray scaled image. 

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");

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)

Please refer to the attached gif file.

Workaround: adjust manually the RadRibbonBarGroup.Margin when the expanded state is changed:

public Form1()
{
    InitializeComponent();
    this.radRibbonBar1.ExpandedStateChanged += radRibbonBar1_ExpandedStateChanged;
    radRibbonBar1.Expanded = false;
}

private void radRibbonBar1_ExpandedStateChanged(object sender, EventArgs e)
{
    if (this.radRibbonBar1.Expanded)
    {
        AdjustMargin(0);
    }
    else
    {
        AdjustMargin(-10);
    }
}

private void AdjustMargin(int top)
{
    foreach (RibbonTab tab in this.radRibbonBar1.CommandTabs)
    {
        foreach (RadRibbonBarGroup group in tab.Items)
        {
            group.Margin = new Padding(0, top, 0, 0);
        }
    }
}

To reproduce:
- Press and hold right mouse button.
- Move mouse cursor outside bounds of the button.
- Release mouse button - the button fill is not correct.

To reproduce:

public Form1()
{
    InitializeComponent();
    this.AllowAero = false;
    this.RibbonBar.Expanded = false;
    ThemeResolutionService.ApplicationThemeName = "TelerikMetro"; 
}

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);