There is no ban, per se, but an absence of a legal recognition of a homosexual union as a marriage. If something is banned, there is usually a penalty for violating the ban.
“If something is banned, there is usually a penalty for violating the ban.”
You may have arrived upon the answer. States such as Texas should institute an actual ban on gay marriage and prosecute those who get gay married in another state and prosecute all those who act in a manner that facilitates the act or continued status of a gay marriage.