Hey Jonas,
I'm sure you've solved this but I figured I'd chime in.
I just bought a Mini and had the exact same problem. I've shot with Mini's before and had never seen this so I was completely perplexed. I contacted a friend who's a Mini owner and he said that the same thing happened to him once, but then it "went away". He suggested updating the SUP or trying a reset. The camera came with SUP 3.1 so I updated to SUP 4 and it has been fine since.
So not sure what was going on exactly but seems like a common bug.
G
