The way it's worded is dickish. The sentiment is understandable. As the group stated; one is orientation and one is gender. They can intersect, but often don't.
I've asked the question as a bisexual woman. Are they ours? Are they their own category? Should we only count transgender people who are also LGB? Does preoperative/postoperative matter? Is a transgender person in a heteronormative relationship the same as a bisexual in a heteronormative relationship since they can both pass?
On certain groups, with a large trans presence, I was told it was transphobic to even question the placement.
On tumblr, oddly enough, I was mainly told, "Yeah, we don't really fit. But we need you."
We saw hostile right on FSTDT. Hostile permeates the darker side of tumblr. Hell, some of my Facebook feminist groups are being taken over by transwomen who have decided they are the ultimate minority women so they get to set the tone for the group. I saw one a few weeks ago argue that talking about things like menstruation and being a feminist mom made the group transphobic.
Power corrupts. And just like most atheists aren't fedora wearing douches most transgender people aren't demanding "I'm a minority of a minority in a minority. Cater to me, bitches!" But just like hostile atheists are disowned so are (perceived) hostile elements of the LGBT community.
Regressive? I suppose there's wiggle room to call it regressive since most transgender people are heterosexual. That's stretching, though.