Incomplete writes?

[KCMO Al]

I was taking shots of an indoor event yesterday and two of the shots were only partially processed. The top 1/3 or so was complete but the image on the remainder was kind of orange on one, and there was no image on the remainder of the other--only gray. I've seen this in film when the shutter speed was too high to synch but I was using TV at 1/100.
I was using a 5D with a 580EXII with the Sto-Fen diffuser. Lens was 24-105L. Is anyone able to diagnose what might be the cause? It was only 2 out of 80 but I'd like to know why.

[PhotosGuy]

I was using TV at 1/100. If you're sure that you didn't accidentally change the shutter speed, then I'd guess a sticky mirror or something like a strap in front of the lens. Did it happen in a sequence of two shots, or were they spread out?

[KCMO Al]

It was on random shots. In viewing them again there were some where the bottom half of the shot was shifted. I'm suspecting either my CF card might be too slow or there's a problem with the body. It wasn't a strap for sure. I was taking shots pretty quickly so the flash might not have cycled completely as well. Thanks for your reply.

[majs]

On my XTI it would do something like this when i have the shutter button partially pressed down and AF locked then I change the zoom (not letting go of the button) and then taking the shot anyway.