Of course it turned out that one of the few new things I've added was the culprit.
Instead of keeping two integer arrays, one for the moves and one for the ordering values, I've mashed them together into a Move-object. Pretty much only for clarity (it shouldn't cause any performance degradation).
Since I didn't use any move ordering at all, ordering part of the Move-object was left untouched. That is until I started to use hash moves which I order as 10,000 (search first in any circumstance) and then -10,000 to mark it already used.
As no other moves received a score, that -10,000 was lingering in the move array and eventually caused no moves to be searched. :)
Well, that's over and done with and using the hash move for ordering gave the following result in my standard mini-test:
1: Mediocre 1.0+ 14,0/20
2: Mediocre 1.0 6,0/20
Barely any statistical relevance really, but I'm happy.
Steady going, on to more move ordering.