If a lesbian liked me because she thought I was a lesbian or a bisexual, uhm, woman, then I'd generally disregard the interest. I've done it before in life, actually, both with a lesbian and a straight guy (who saw me as a girl).
If, however, she was a lesbian who was making an exception and saw me as a guy and treated me as such then I would make an exception as well and, if things seemed mutual, would see where things went. If she still wanted to identify as a lesbian then fine by me, so long as she did not think of the relationship as a lesbian one.
I've actually even had problems in a past relationship related to being seen and treated and referred to as FTM opposed to just M, I'm just not comfortable with it; I know I'm FTM, but I identify as a guy and want to be treated as such. So I'm definitely not going to be comfortable being seen, treated, and referred to as a woman.