A lot (if not most) of gender behaviors are cultural, and thus arbitrary. And maybe not picking up on non-verbal cues as well as average means you'll have to learn it a little more consciously. It doesn't mean there's anything wrong with you.
When I was a teen I noticed the leg crossing thing, and eventually got into the habit doing the ankle-to-knee style (though I've seen males do it the other way, also; it's just a lot less frequent). I found there are a lot of little rules that like that and some I don't worry about; after a point it became endless all the little things I was doing 'wrong.' At a certain point you have to balance how much it costs you (mental & psychological energy) with how much weirdness from others you want to deal with.