A couple possibilities:
1) They over-filled the tranny and the excess 'vented' through the vent.
2) The weak hose is about to let loose, catastrophically.
3) They missed placing a sealing washer under one of the hoses.
4) Maybe someone forgot to tighten the drain plug.
5) I'm a complete idiot for thinking I could cover all the what-ifs in three lines or less....
Beav