Shutter half way to focus, recompose not working

[ballybay]

Hi! I just recently ungraded from the 5D Mk ii to the iii.  I know the focus system is pretty sophisticated on the iii, but a simple half press of the shutter to focus, and then holding while I recompose, isn't working... the lenses are refocusing elsewhere in the frame - usually at the longest distance. I've tried it with both my 24-105mmL and my 300mmL, and guess it is the same with all my lenses. This is also happening with the back-button focus.  I've also lost the beep when focus is achieved.  I believe it is something I am doing in the Case settings or elsewhere that is causing this because when I clear the camera settings, I have this function back. I'd just like to understand what I am doing that is causing the inability to recompose the shot after focusing.  THanks!

[ballybay · Accepted solution]

.... actually, I think I've figured it out. I was shooting birds in flight and had the cam set to Case 5, and had made focus a priority. This must have caused the camera to refocus on a half shutter press when I went to shooting something else without changing the focus settings.