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)

Allow small elements, e.g. RadTrackBarElement or RadProgressBarElement, to be added to RadRibbonBar groups at design-time.

RadRibbonBarGroup consists of two FillPrimitives (in addition to the main FillPrimitive). These fills should be exposed to the user, so that s\he can tell what their colors should be.

Resolution: 
RadRibbonBarGroup consists of two FillPrimitives which are exposed: GroupFill and BodyFill. You can set their color using the following code snippet: 
radRibbonBarGroup1.BodyFill.BackColor = Color.MediumPurple;
radRibbonBarGroup1.GroupFill.BackColor = Color.MediumSeaGreen;

To reproduce:
  Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        For index = 1 To 10
            Dim Temp As New RadButtonElement
            Temp.Image = Image.FromFile("C:\Program Files (x86)\Telerik\RadControls for WinForms Q3 2012\Examples\QuickStart\Resources\1RibbonMenuNewMagenta.png")
            Temp.TextImageRelation = TextImageRelation.ImageAboveText
            Temp.ImageAlignment = ContentAlignment.MiddleCenter
            Temp.Text = "Test"
            RadRibbonBarGroup1.Items.Add(Temp)
        Next

        'workaround
        'RadRibbonBar1.RibbonBarElement.ElementTree.ApplyThemeToElement(RadRibbonBar1.RibbonBarElement)
    End Sub

To reproduce:

Add a RadRibbonForm and set the theme to Office2013Light. Start the application and click the backstage button. Click the close button and you will see an exception.

Workaround:

this.RibbonBar.BackstageControl.BackstageElement.TitleBarElement.CloseButton.MouseDown += TitleBarElement_MouseDown;
void TitleBarElement_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
    this.RibbonBar.BackstageControl.BackstageElement.TitleBarElement.CanManageOwnerForm = false;
    this.Close();
}

To reproduce:

Create a RadRibbonForm and set its ApplicationMenuStyle to BackstageView. Start the application open the backstage, click the maximize button and then again to set the Form back to normal. You will notice that the Form cannot be set back to normal.

Workaround:

Manually change the WindowState of the Form.

this.RibbonBar.BackstageControl.BackstageElement.TitleBarElement.MaximizeButton.MouseDown +=MaximizeButton_Click;

void MaximizeButton_Click(object sender, EventArgs e)
        {
            if (this.WindowState == FormWindowState.Maximized)
            {
                this.WindowState = FormWindowState.Normal;
            }
            else if (this.WindowState == FormWindowState.Normal)
            {
                this.WindowState = FormWindowState.Maximized;
            }
        }

To reproduce:
- Add ribbon bar with a few buttons subscribe to ScreenTipNeeded event and show different text for each button.
- Collapse the tabs by clicking the collapse button, the expand a tab by clicking its name.
- You will notice that the ScreenTipNeeded event is not fired.

Workaround:
Create separate screen tip for each element:
RadOffice2007ScreenTipElement button2Tip = new RadOffice2007ScreenTipElement();
button2Tip.CaptionLabel.Text = "button 2";
button2Tip.MainTextLabel.Text = "button 2";

radButtonElement2.ScreenTip = button2Tip;

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;
    }
}

RadRibbonBar, the back stage button in not exposed in style builder.

If you maximize an mdi child form in a mdi parent, the buttons of the child form appear in the title bar of the parent form, but not in the tabstrip of the RadRibbonBar contained in the parent form.

If you press the Alt key once, you get the KeyTips displayed. If you press it once more, the KeyTips should become hidden and the focus should be returned to the previously focused control.

When you set the EnableKeyMap property to false, this setting is not serialized in the designer.

When you open the content popup of a collapsed group and click on a button that shows a dialog form, the popup stays opened.

Go to Examples app, section RibbonBar >> FirstLook. Decrease the size of the main Examples form. Dropdownbuttons will appear instead of the actual content in RadRibbonBar. Open one of these buttons and click on the empty space area of the popup. The popup will close, but is should stay opened.

Go to the Examples, RibbonBar >> FirstLook. Decrease the width of the main form. Now open the 'Size' popup of RadRibbonBar. You will notice that the Size dropdown button is not properly aligned i n the popup.

The Click event of the ExitButton and OptionButton is fired twice. If you subscribe to the ButtonElement of the ExitButton and OptionButton (which are RadMenuButtonItems), then you will get the click event fired just once.

It will be nice if RadRibbonBar has the QuickAccessToolbar property exposed in the property grid of Visual Studio, just like ExpandButton, ExitButton, etc.

The text of the quick access buttons looks doubled when an Office2010 theme is applied, and the Aero mode is turned on.
Update: This could be worked around with TextRenderingHint, BUT the font will not look ok when the mode of the form/titlebar is not Aero

Pressing the ALT key should displays the Key Tips and moves keyboard focus to the RadRibbonBar by pressing any of the typical keyboard navigation key (i.e., TAB, SHIFT+TAB, ARROW RIGHT, ALT+ARROW, DOWN, SPACE BAR, etc.)