After some tests, it
seems that only postbit and postbit_legacy are concerned... I say "seems", as I haven't tested all templates, of course, but nearly 20 of the most common ones. All 20 are giving correct results with $vbulletin->userinfo variable.
Btw, I find it rather "good" that only those templates are concerned, as it may have to do with some special treatment for them
If I get no response or no clue from here, I will try to investigate deeper.