I don't see why it matters what other genders the person is into, it's not like they're going to be cheating on you with someone of the other gender. And if they did, then it would be bad whichever gender it was with...
I mean personally, I can see how it might bother some people - I'm dating a bi girl, and she does talk about guys a lot more than girls, in fact, she never really talks about girls - but then that could just be down to not wanting to "out" herself too much. I don't know. It doesn't bother me, because she's dating me and not anyone else, and the gender of the people she isn't dating doesn't concern me all that much.