My manual says exactly what Shy says.
I have a mate that regularly jumps out of the back of one in Saudi and has to freeze all the way up to drop altitude because they wont open the door inflight, so that's one air force using that restriction.
I'm really curious about this limitation because it seems like quite a restriction for a military helicopter.
Ha ha, I'll keep the 'vacuum cleaner effect' in mind, thanks for the warning.