After looking into your problem a bit deeper it seems there are certain apps that may override these settings and force screen locks. There is also different versions of android each with different menu settings.

So I would say the best option for you is to go through a process of elimination by first finding out what version of android your phone is using and doing a search for screen lock during call settings based on that version. Then if that does not solve the problem begin removing unnecessary apps and then one by one disabling the apps you need until the problem is resolved.

Other than that, maybe the other comment about trimming around the camera might fix the issue.

Sorry I can't be of more help, I hope you resolve the issue.