Its's been a while since i have used CM7 but i think i remember this problem. i could be wrong but i think it had something to do with deep sleep and there was a flash-able zip that fixed it. like i i said it has been a while since i've used cm7 (over 7 months now).
What cm7 rom are you using? i think Mrom had this bug fixed. Mrom was the last cm7 rom i used and to me (and this is only my opinion) it was the most stable for me
Current Phone: Google Nexus 4 - 8GB, Stock Android 4.4.4 Rooted
Previous Phones: Nokia (Can't remember the modle), Motorola L6, Motorola L7, Motorola Backflip MB300, Motorola Atrix 4G