[BUG] No incoming calls received on any CM12 Radio when screen locked for 5 mins topic

After so many tests, i can finally confirm this problem.
Basically, in the last week or so, i have been missing almost all incoming calls because of this problem.

I found, even with the newest nightly 02072015,
all CM12 Modem update will cause my OnePlus to not responding to incoming calls after screen lock for more than 5-10 minutes.

My area does not have the best reception, normally 1-2 bars, but i rarely missed a call because of it.

all test are done with clean installation after revert to stock. put in lock for about 5-10 mins.
My test result:
CM11S + 44S Radio, 3 test calls, received all. Caller side ring twice until phone respond.
CM11S + 38R Radio, 3 test calls, received all. Caller side ring 2 - 3 times until phone respond.
CM11S + CM12 Radio, 3 test calls, received one call. 2 not received, Caller side ring twice then went into voicemail.
CM12 + CM12 Radio, 3 test calls, none received, Caller side ring twice then went into voicemail.
BlissRom2.0 + Bacon_firmware_update, 3 test calls, none received, Caller side ring twice then went into voicemail.
BlissRom1.8 + 44S, 3 test calls, received all. Caller side ring 2 - 3 times until phone respond.

This problem will not occur if the phone is "freshly" locked.