4.0.1 baseband 01.59.00 behaving strangely

my iphone 4 running 4.0.1 with baseband 01.59.00 has been jailbroken and unlocked (using ultrasn0w 1.2.3) for a while now. for the most part it works great. however, once in a while after i power the phone off then on, it does not recognize the sim and i had to re-install ultrasn0w. it seems as though this version of ultrasn0w is giving me the tethered unlock. will someone please verify this for me. if so, how do i fix this permanently without upgrading to a higher version, say 4.1.x or 4.2.x

** updates
no one has any idea why every time i power off the phone, i had to re-install ultrasn0w, as if to unlock again, to get signal for my SIM (other than AT&T)