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)