It's possible that you have the first setting set to require the button press to move around the corner, which would explain why my suggestion doesn't work. If you try tinkering with the settings and still can't get it to work, I'd suggest trying to take a short video of you not being able to do it and then post up a help request on the official forums with the video proof included.Not sure if everyone knows this, so I thought I'd share.
If you go into settings/controls, you can change 2 settings that helped me a lot in fire fights.
The "move around cover corner with button press" setting I changed to YES. Now you don't automatically move around a corner exposing yourself. You must press and hold A to move around the corner.
Also, i set "movement can exit cover" to NO. Now I don't accidentally move out of cover and get shot. You must press A to exit.
This helped me a lot...I hope it helps some others