I'm not sure if this counts, but I'll throw it in because there's a discrepancy:
The table of the Ultimate Magus PrC states that at levels 1, 4, and 7, you advance the casting class with the lowest class level, but the text states that you advance the class with the lowest caster level (which opens up Practiced Spellcaster, Illumians, and the like).
Now, I don't consider it abusive per se, but the discrepancy leaves some people wondering what WotC's actual intent was for the class. It's just technically a typo that's caused confusion for some. I've always used the way it's presented and go off of the text.