I have to say, I think it's a little unfair to say that if a trans woman behaves the way many cis women do - as has been mentioned on this thread, there are tons of cis girls and women who don't wear dresses or makeup very often - it's "masculine." There's a huge gray area between hyper-feminine and masculine, after all.
(I'm actually pretty femme, just not in a way that involves a lot of dresses. I'm way more femme than my wife, that's for sure!)