When a floating image is moved out of the viewport it disappear and only its borders stay.

Workaround: Set padding: <telerik:RadRichTextBox LayoutMode="Flow" Padding="0 0 0 500" />

Steps to reproduce: 
1. Open RadRichTextBox application

2. Set the layout mode to Web

3. Insert an image and set its text wrapping to Square (use the context menu when you click with the right mouse button on the image)

4. Move the image in a way, part of the image will go outside of the viewport

Observe: Image disappears, only the image adorner stays. Sometimes when you insert another image after the bug has occurred, the bug can be reproduced even without step 4 from the above described.

Expected: The image shall not disappear and it shall be placed near the end of the viewport, but not outside it.