One of the (many) bugs I've discovered while working with Mediocre the last month was that it uses the wrong piece square tables for the most part of the games.
Mediocre has two kinds of tables, for opening/middle game and for endings.
The bug was that Mediocre changed to ending tables after the opening phase. That is awarding moving the king and queen into the center etc. in the middle game...
The weird part is that this greatly improves the performance of Mediocre. "Fixing" the bug in v0.334 and running a match against a non-fixed version results in a clear victory for the latter.
I assume this has to do with the mobility/piece square features not being scaled as they should.
I will have to take a long look at the evaluation again since this is clearly a bad thing. :)