I've determined something on my 5D is having trouble w/ shutter speeds over 2000th/sec. At 1/2000, everything is fine. By 1/4000 there is noticeable shading across the top of the image. By 1/8000th the frame is about 95% covered.
I typically shoot interiors and portraits with this camera, seldom (if ever) sports or any other hi-speed applications. In fact, I've shot with this camera for months and only noticed it by accident this weekend when I had a f/1.8 lens on shooting in Av.
Here are my questions:
1) Is this a shutter speed issue, or do you think it's my mirror (flip up) that is having a problem?
2) If it's a shutter problem, do you think it it is atually happening across ALL shutter speeds? In other words, if I am shooting at 1/1000, do you think I'm really getting 1/1000 or is it actually slower than that?
3) If I'm only shooting slower than 1/2000 anyway, do I even need to worry about it?
Thanks...

! canon fixed the shutter under warranty and the round trip took 8 days.
everything is much more expensive here. 

