lock screen always toggles between two variants
Unfortunately I don't think you're going to find a setting change to fix this. It's likely a bug in the ROM, or the lock screen or cLock apk(s). I'm also running CM10.1 on my phone (LG Nitro HD) and I can't even get the cLock app to change to using an analog clock (vs. the Digital). Even after multiple reboots and confirming that indeed I have the right settings in Settings->Lockscreen.

Some rudimentary net searching and you can see issues with the lockscreen on CM10.1 is not unusual.