Is it illegal to list a house behind spouses back?

My girlfriend used to live in Texas, after some meaningless surfing she happened to find a site that showed her ex husband had listed the house for sale while they were still together; although admittedly around the time things started going sour. She was listed on the deed. In the divorce she gave up her interest in the house, got her belongings, no spousal, and reduced child support (visitation/travel) because she moved home to Nova Scotia, Canada. My question I guess is, was it legal for him to list their house without her knowledge. Secondly, via another search site, my girlfriend is still listed as married to her ex, residing at same residence, and her oldest daughter is listed as residing there as well (which is accurate), but her youngest, who lives with us in Canada is not listed as a relative at all, let alone where. He makes a good income, he works for a financial firm, fairly high up. I'm not a gold digger, but I'm divorced, have dependents I pay support for, based on my income, I make good money too. It just bothers me when things get tight financially from time to time, he cries like a baby. It's his daughter that looses out, she's entitled to her past lifestyle to an extent based on his income, isn't that how/why support percentages of salary are set? We all ready had to hire a lawyer in Texas, from here, as last summer he tried to keep her after summer visitation, he had her registered in school and was denying it to the bitter end. We ended, getting her home (NS).....but the temporary orders are still hanging, supposed to be finalized by now. Now he's balking at the rate increase in support, because the oldest is over 18 now, since February, and his support has not been adjusted. Now that she is in Texas for Christmas vacation, he finally somehow gets the request for finalized papers from his lawyer, 1/2yr of more after our lawyer sent them to his. I don't trust him, it doesn't seem right (his listing the house).