The Validity of Marriage after Transition in the US

From Indiana Public Media:

Sanders says the ruling will likely serve as an example when this issue comes up in other courts.
“Around the country there are probably more couples in this situation than many people realize.” Sanders says. “That is a couple who was male and female at the time being married and then one of them transitioned genders and many of them wished to stay married.”
Sanders says couples in this situation need confirmation their marriage won’t become void automatically if one of the parties undergoes a gender change.
Sanders says the Indiana appellate court’s decision is the first one documented involving gender change within a legal marriage. 

Actually, I think there's another case in Florida.

Q: Is a marriage still valid if one spouse transitions
later on?

A: Marriages remain valid if they were valid at the time they were entered into. The government cannot retroactively invalidate a marriage because of a change in eligibility criteria that occurs after the marriage is entered into. Not even the federal Defense of Marriage Act (see sidebar for more about DOMA) should affect couples who are already married and were eligible for marriage at the time they entered into that relationship.
It’s an important principle to defend, especially in the face of openly anti-transgender policies and sentiments. That was the situation, for example, in 2007 when Lambda Legal represented a transgender man in a Florida alimony case known as Roach v. Roach n.k.a. Silverwolf. Julio Silverwolf(formerly Julia Roach) transitioned from female to male after 18 years of marriage to Lawrence Roach.
When the couple were divorcing, Roach argued that he shouldn’t have to pay alimony because Silverwolf was “legally dead” as a result of his transition and because Florida does not recognize marriages of same-sex couples. But the court upheld the alimony agreement, basing its ruling on the determination that the marriage was valid at the time it was entered into.

That's from Lambda Legal's TRANSGENDER RIGHTS TOOLKIT: A LEGAL GUIDE FOR TRANS PEOPLE AND THEIR ADVOCATES TRANSGENDER PEOPLE AND MARRIAGE LAWS

I have a letter from the Australian Attorney General (at the time) confirming that this is also the situation here. If legally Male and Female at the time the marriage was contracted, the marriage remains valid. Unfortunately there's caselaw stating that Intersex people, regardless of birth certificates or other documentation, are neither male nor female for the purposes of marriage, and so may not marry anyone.