When Motion is running, and the Video RAM (VRAM) in your graphics card becomes full, it's possible for the display of objects in Motion to become corrupted. This can occur on video cards that meet the System Requirements for Motion, and is more likely to occur on cards that have a relatively low amount of VRAM.

This issue only affects the display of in-project imagery. In other words, Motion's GUI elements are not affected. Also, if this issue occurs, the display of other applications and Mac OS X elements are not affected.

Workarounds

In the interest of minimizing occurrences of this issue, try these actions to make more VRAM available to Motion:

Quit as many other applications as practical. This issue can especially be affected by applications that process or display graphics (or otherwise vie for VRAM).
If the project uses large still images, try changing the setting for Large Stills in Motion Preferences to Down-Res to Canvas Size. Using fewer and/or smaller images may also help.
Use fewer and/or smaller video files.
Use fewer particles in particle systems.
Use a lower bit depth setting in Project Properties.
Occurrence of this issue can be somewhat random. It may be worthwhile to save the project and quit Motion, and then open the project again.
This document will be updated as more information becomes available.