Well the reason for this misunderstanding should not be to tough to ID. Jerry Springer, Maury, Phil (no longer a Dr.)... are good places to start. But simply by the virtue of GLB and T as our associated group you can't really brame people for making a connection. I would hope everyone here agrees that Gender Identity and Gender Expression are unrelated to sexual preference yet as a group we are included in with those variations. Not a big jump for the uninformed to think they are all together therefore they must be nearly the same.
The best thing is to use the opportunities each of us get to correct this misunderstanding in a respectful clear way. Personally for me I think the mixed gender community get little benefit from this association but I understand why they are grouped together. The benefit is a greater number for both causes but the drawback is the line get really blurry to mainstream.