[@_ck_ Participant 18 years, 2 months ago]

Ah apparently Detective’s method is for sites running WP at the same time as bbPress (not just integrated, running within each other – which I do not recommend). So this won’t work for most people.

I solved the problem by forcing all registration links to go through WordPress but obviously that’s not a perfect answer (and needs core hacks).

So this problem needs to be revisted again