Crew calling out random numbers

Ok, this must be a bug. I'm still doing the tutorial missions, since I just started with this game. I'm doing the convoy one again, and I've been playing about 1 1/2 hour or so. Sank a destroyer and a few freighters. But now my crew starts calling out random numbers. Like: One, Five, Eight, Six, Nine etc. etc. over and over.
First I thought, ok maybe theyre getting tired and this is the game's way of telling me my crew is losing it. I checked the Crew panel, and I have some injured crew, but most health is not lower then 90, and morale is normal, so what the heck is going on?