Agreed, I think it is because male teachers tend not to take a lot of crap from students where as women tend to be more patient.
I just think it's a good and proper bias to have, a natural caution that we're born with: that the opposite sex has much to offer, and much to be desired -- but it is very dangerous and can hurt you terribly.
Both males and females are right to be wary of each other. That's why boys and girls play separately, then slowly come together as they mature and find trust.
To a point I'd agree with you, but I think that males and females interpret different kinds of behavior as acceptable. Male teachers tend to dislike the giggly, bitchy, passive-aggressive, arrogant behavior that girls offer up as discipline problems while they are more forgiving of the boy-type misbehavior. Female teachers are more forgiving of female misbehavior and tend to consider the normal squirminess and inattention of boys as meaning that the boys are misbehaving, perhaps even ADHD.