It sounds like you had the phone unlocked but not by using a vendor-provided code? Not sure what the difference is to be honest, but I have one GT-i9000M that was unlocked by Bell and it never re-locks compared to the other GT-i9000M that I unlocked myself using an app and it re-locks itself. It's mainly attributed to flashing the CSC file.I only did the "Phase R: Flash UGKG3" portion, as I would like to get the phone working 100% again before making any other modifications... I was wondering if anyone else was asked to "Confirm Password"?
If you follow through "Phase 2B: Flash a rooted kernel" and then install this app: https://play.google.com/store/apps/details?id=com.helroz.galaxysunlock&hl=en you should be able to unlock the phone once again and for free.