This is tested and reproducible in the Office2016 and Material themes. Probably it can be reproduced also with other new themes which use glyphs.

The CPU goes high because the RadRibbonGroup contains a GroupChrome element which has a TextBlock with the GlyphAdorner.ShowGlyphInDesignTime property set to True. 

To resolve this:

1.Extract the ControlTemplate of the RadRibbonGroup control.
2.Extract the ControlTemplate of the GroupChrome control.
3.Find the TextBlock element in the GroupChrome ControlTemplate.
4.Remove the telerik:GlyphAdorner.ShowGlyphInDesignTime  setting from the TextBlock
5.Set the Template of the GroupChrome in the RadRibbonGroup ControlTemplate to the custom GroupChrome template.
6.Apply the custom RadRibbonGroup template. 

Several galleries in collapsed state. Open rightmost so that its popup is outside wpf window.

Then resize the window so that gallery goes into large state. The height of the RibbonGallery is incorrect and smaller than expected.

Workaround is to set MinHeight to (for example 67) to all RibbonGalleries.

This is reproducible only in the FluentTheme. Setting the RadCollapsiblePanel.SmallButtonsPerColumn to 3 does not make any difference.  

The workaround is to set a higher value for the ContentHeight property of RadRibbonView, for example 120px.

The fix for this issue will be available with LIB (version 2018.3.1203) published on Monday, 3-rd December, 2018. 
 

Scheduled for:
The fix for this issue will be available with LIB (version 2019.1.121) scheduled for publishing on Monday, 21st January 2019.

The property allows you to align the minimize, maximize and close buttons to the left or the right of the window's header. Currently, this is implemented to work only for RadWindow. Add support also for the RadRibbonWindow

Every KeyTipControl is placed inside a Popup. Expose properties which could control the Popup position.

When opening Backstage using KeyTips service, NullReferenceException is thrown when the backstage items have also had KeyTips set. 

When the RibbonBackstage is open and then a RibbonBackstageItem is clicked to close the backstage, the ApplicationButton's FluentControl pressed state effect remains visible in the Fluent theme.

The ribbon tab doesn't get selec if you click in the exact middle of the header of RadRibbonTab.

To work this around, extract the ControlTemplate of RadRibbonTab and move the Grid with x:Name="ContentPanel" before the Grid with x:Name="HeaderPanel".

The HeaderVisibility property of RadRibbonTab doesn't work when changed at runtime.

A workaround is to use Visibility property of RadRibbonTab, instead of HeaderVisibility

When a RadRibbonSplitButton or RadRibbonDropDownButton are defined in the ApplicationMenu, their drop down content does not receive proper focus. This can be observed in the Office2016 theme. 

When the "Automatically Hide the taskbar in desktop mode" windows setting is enabled and the RadRibbonWindow is maximized, it exceeds the screen area. 

When hovering over the buttons inside the application menu, the background color changes to dark blue, but the button text stays black, which is very hard to read.

Setting the MinimizeButtonVisibility has no effect in some themes.

When the EnsureHandle method of WindowInteropHelper is called on a RadRibbonWindow instance that is not shown the UI is frozen. 

When the Windows OS auto-hide taskbar feature is enabled, the RadRibbonWindow is clipped and offset on the top and left sides. This reproduces only if the window is maximized initially. Changing its state afterwards resolves the visual glitch. Also in order to recreate this the IsWindowsThemeEnabled property should be set to False, in order for the ribbon window to use its Telerik theme, instead of the Windows one.

When the Visibility of the RadTabItem is set to Collapsed the keyboard navigation does not work as expected. 

The backstage of the RadRibbonView cannot be opened when the control is placed inside a WinForms application.