Despite what many people outside the USA believe, it is by no means a single country with a single set of laws and a single set of cultural attitudes. Sometimes this can be a good thing, but sometimes the differences in laws between states, or even between parts of the same state, can cause an awful lot of confusion. Jenny Boylan has an article in the NY Times talking about how the current mishmash of legislation regarding gender changes and same-sex marriage affects trans people. Here she quotes a lawyer from one case that came to trial:

Taking this situation to its logical conclusion, Mrs. Littleton, while in San Antonio, Tex., is a male and has a void marriage; as she travels to Houston, Tex., and enters federal property, she is female and a widow; upon traveling to Kentucky she is female and a widow; but, upon entering Ohio, she is once again male and prohibited from marriage; entering Connecticut, she is again female and may marry; if her travel takes her north to Vermont, she is male and may marry a female; if instead she travels south to New Jersey, she may marry a male.

It really is a mess. Hopefully the USA will eventually get things sorted out at a federal level.