I have the 7D and have never experienced this phenomenon.

A couple of things to try:-

• Set camera settings back to factory defaults. (There is a menu option to do this).

• Wipe all custom function settings (not included in the above, I don't think).

Try to replicate the problem after each step above. If it still exhibits the problem:-

• Remove the main battery. Then in the battery compartment, you will find on the side a 'slide out' bit of plastic containing a little flat round battery. This is usually responsible for keeping the date/time and settings on the camera when you remove the main battery. Remove this flat round battery. Put the camera aside for no less than one hour. Then when the hour is up, replace the flat round battery, replace the main battery, and turn on the camera. Note you will need to re-set the date and time etc as if it was brand new. Try to replicate the problem again.

If the problem still occurs I would take it to an authorised Canon dealer who should be able to send it back to Canon on your behalf to be checked out. It sounds like it may be an issue with your camera. If it is less than one year old you should be able to get it fixed or replaced under warranty.