Official problem with 7D

Canon USA released today a service notice which says there is an issue with images captured in continuous shooting mode which, under certain conditions, contain barely noticeable traces of the immediately preceding frame. A firmware update is planed to solve this issue.

Click here to read the full service notice.

Firmware Update

Canon releasead a firmware update for EOS 7D. The new firmware 1.0.9 is for cameras with firmware version 1.0.8. The fixes releasead are:
1. Improved AF accuracy while in Live View mode.
2. Fixed abnormal colors in movies shot under some rare circumstances.
3. Corrected a problem where the shutter cannot be releases at certain timings, wile using camera's built-in flash or an external speedlite.

For details see Canon Japan official firmware site.