I sorta think that maybe this is comparable to the fact that more often than not, I am my true self in my dreams - I am male. Other times, it's like my gender doesn't exist or something...but even then it's like I am still treated by others in the dream as male. It's very rare that my dreams present me as female. It's been like that for so long, I really can't remember when I was always female in my dreams - or if that was ever the case.
We have no control over our dreams...so I would think that if in my dreams I am male, it must be because that is the way I think of myself when I'm not asleep. As if it's... normal.
-Michael