In that light, ditch the belly check.
On it. That's this evening's job
It's not an outright bug in the first place, unlike exits accepting dying* lemmings
Even though Amiga doesn't have DD and DOS does (and I'm generally more of an Amiga purist than a DOS purist), I still think DD should be a legit mechanic. If the lemming makes contact with the Exit's trigger and they're still visible, they should exit. Lemmings that fall onto traps from a height are still affected by the trap (confirmed in Amiga, at least), so why not exits?
Furthermore, the "backroutes" that DD introduces wouldn't
be backroutes if DD were an accepted, intended mechanic. So, in SLX, it's an accepted, intended mechanic - not a bug!
Anyway, I could debate DD all evening, let's concentrate on these Builder mechanics instead...