While I'm bisexual and trans, I've experienced more severe discrimination and violence from within the LGB community due to my trans status as opposed to outside it. When straight cis people are more understanding and respectful of you as a person than people who are supposedly supposed to be part of your community, it becomes quite...How should I put this? Irritating? No, I'd say it's more that it sours the thought of being associated with them for *that* aspect of my existence.
I participate with LGB folks for issues of sexuality, etc, but never my gender. I feel that lumping in gender identity and sexuality together can be problematic, especially considering how many don't even know what the T stands for and ignore trans issues in favor of LGB ones. Not to say that these aren't important, because they certainly are, but it becomes grating to be thrown in under the label when your rights and safety do not matter to the majority of the community.
Big name equal rights groups also have long histories of transphobia and shoving transgender members of the community under the bus, and while some may seem apologetic to avoid controversy, the fact is that many do not change their ways and continue to silence trans people who speak up against them. These are the main reasons I have such disdain for having the T with LGB, despite technically being "both", and often prefer to think of each community's issues separately.