They shouldn't bother to, you still have all the same splash screens right, it wasn't flashed with a new rom? Just checking quick.. Here is a stock rom:
http://downloadandroidrom.com/file/GalaxyS2TMobile/unroot/SGH-T989-UnRoot_ROM_Zedomax.zip
Here is his vid on restoring:
How to Unroot T-Mobile Galaxy S2! [SGH-T989] - YouTube
Haven't used it but it seems to be a good go. Are you on a SGH-T989 or the international unit, I think I never asked that...