Thats interesting. I always get the return BP in SIN (or another city if transitting through SIN) and just go straight upstairs on arrival. The transit desk is actually on the arrivals level just before immigration - not sure why they couldnt issue TG BP there?

While there's generally security/immigration folk standing near the stairs/escalators, sometimes they dont bother checking anything (not even BP), other times carryon is screened and BP checked.

IIRC I've seen mention that asians may be treated differently.