My wife has the Canon EOS Rebel T2 35mm SLR. We're having a problem when she's trying to adjust the shutter speed. She'll get it up to, say, 1/250 second exposure, and the next "click" will put her back down to, say 1/60 second exposure instead of going to 1/500 second exposure. This appears to happen in both Manual and Shutter Priority (Tv). Is this a problem with the camera, or is the camera trying to correct for lighting to get a proper exposure? Thanks for any help.