Nevermind, solved it!
I'll leave the post for others to see, though.
I had moved the stop point forward to position the aircraft accordning to the Flytampa parking aid. Apparently, that confused the forward baggage train, so this behaviour occurred. The solution was to move the baggage train about the same amount as the stop point.
Strange, though, that it only affected the unloading - even if the baggage carts come from afar, when you request boarding.
BRGDS
Sven Sorensen, EKCH