upgraded to color OS 2, hated it, installed TWRP and CM11 and ended up with the same troubles as the thread author here...
I reset to factory settings, downloaded the color OS 1.24 image, flashed that, reset again, and reflashed CM11.
now the proximity sensor is working, and I don't have to ask the people i call to hang up for me /use the power button for hanging up.
with regards to the battery drain - it looks better already, but i'm going to look it over during the next couple of days. thanks for posting your solutions!