[BirdOPrey5]

Are you sure you are using the version you linked to? After reading through that entire thread (because the original mod was poorly written and giving database errors and other screw ups) I found someone else had released a 4.x version which fixes most of the major bugs:
https://vborg.vbsupport.ru/showthread.php?t=229473

But still has some of its own... This new mod is definitely better than the original you linked to but the basic problem is vBulletin is missing a hook, there should be a hook register_activate_complete but there isn't. If there was it would solve many problems...

I'm torn between releasing what I have which only will work reliably when email confirmation is off (which I would never do on a live forum) and just merging both mods into 1 new one I can release since the original coder gave his permission for anyone interested to re-use his code.

How exactly are you using this mod? (Do you require email conformation on registration? Do you make the welcome thread on registration or on activation?)