I've been working with two different Canon EOS 5D mark III cameras, and had the same problem with both.
When auto-focusing I have two kind of indicators when the image is focused on a certain point.
- the audio beep
- visual indicator on the focus point (the light/square on the selected focus point "blinks" red for a moment)
Altough I hear the beep every time the camera auto-focuses, the visual indicator does not show (or at least I cannot clearly see it) every time.
I'm not sure if this is related, but I just did a short test (indoors) pointing the camera in various directions with diffrent light coming from different directions, so I'm guessing there's something to do with the lighting, but I might be wrong... In the test when the visual indicator worked on certain points in the room, it worked in 90% of retries, while when trying on other points it almost or never worked...
Do other Canon 5D Mark III users have the same problem? Is this a matter of a setting which I need to modify, or is there a problem with the camera?