crazyhouse drop with instand check mate

I was checkmated by a drop instandly. I thought this was forbidden. I am confused. Is this a bug or did I understand the rules the wrong way.

@raubstein This is actually allowed. This is part of the rules:
a check that would result in checkmate in standard chess can be answered in Crazyhouse, if the defender can play a legal drop that blocks the check.

Drops resulting in immediate checkmate are permitted.
Pawns may not be dropped on the players' 1st or 8th ranks.
Promoted but captured pawns are droppe