Hi, i face the same problem, after a call some time screen went off, nothing can bring it on again
But some time is just fine. Last time i was using CM7 on my HTC Aria without facing any problem
This problem occur after i swift to CM7.2 and also CM9 ICS.
So, i assume my Proximity Sensor is in good condition (Working good in Previous version CM7). So, the problem might cause by some setting... so i try with some adjustment....
First, i turn the phone sleep policy to 30min. Coz from my experience, short call will normally won't cause the screen off after call, only long call will. So i assume this is cause by the screen off policy. just go to setting---> Display--->Sleep---->30min(Maximun. coz my device don't have any option to turn this off)
Second, i think this might be cause by the automatic backlight option! If u are using custom light level (CM7/9 normally come with custom light level setting). jz TURN IT OFF/ OR LEAVE THE OPTION UNTICK.
After i did this 2 adjustment, the problem had been solve. 1hrs call still manage to keep the screen on bck to normal
i hope my experience help u all ^^