We have observed this issue only in Lightswitch projects - the images are shown only if they are added to the visual tree on start-up. The problem does not occur when there is a RibbonUI, because the ribbon includes the images in XAML.

The workaround we can suggest to you for now is to declare the images in XAML. This means, you should have a line like this for all images which are used in the SelectionMiniToolBar and the ContextMenu in your .xaml file:

The images can be collapsed or with Height/Width set to 0.

Here is the list of the used images in theSelectionMiniToolBar and the ContextMenu (please note, you should add in the beginning the  "/Telerik.Windows.Controls.RichTextBoxUI;component/Images/MSOffice/16" string, as a part of the path to the following resources):

SelectionMiniToolBar:

• font-increasesize.png
• font-decreasesize.png
• outdent.png
• indent.png
• bold.png
• italic.png
• underline.png
• aligncenter.png
• highlight.png
• FontForeColor.png
• list-bullets.png
• list-numbered.png

 ContextMenu

• cut.png
• copy.png
• paste.png
• inserthyperlink.png
• FontProperties.png
• ParagraphProperties.png