I think it says that after joining the US - Texas was a state of the US even when they erroneously thought they had seceded. But I bet the Republicans still believe Perry.
~Texas vs White~ ~1869~
When, therefore, Texas became one of the United States, she entered into an indissoluble relation. All the obligations of perpetual union, and all the guaranties of republican government in the Union, attached at once to the State. The act which consummated her admission into the Union was something more than a compact; it was the incorporation of a new member into the political body. And it was final. The union between Texas and the other States was as complete, as perpetual, and as indissoluble as the union between the original States. There was no place for reconsideration or revocation, except through revolution or through consent of the States.
Considered therefore as transactions under the Constitution, the ordinance of secession, adopted by the convention and ratified by a majority of the citizens of Texas, and all the acts of her legislature intended to give effect to that ordinance, were absolutely null. They were utterly without operation in law. The obligations of the State, as a member of the Union, and of every citizen of the State, as a citizen of the United States, remained perfect and unimpaired. It certainly follows that the State did not cease to be a State, nor her citizens to be citizens of the Union. If this were otherwise, the State must have become foreign, and her citizens foreigners. The war must have ceased to be a war for the suppression of rebellion, and must have become a war for conquest and subjugation.
Our conclusion therefore is that Texas continued to be a State, and a State of the Union, notwithstanding the transactions to which we have referred. And this conclusion, in our judgment, is not in conflict with any act or declaration of any department of the National government, but entirely in accordance with the whole series of such acts and declarations since the first outbreak of the rebellion.
http://www.law.cornell.edu/supct/html/historics/USSC_CR_0074_0700_ZO.html