Not sure about the mermaid/alien hybrids, but all the other hybrid types are buggy as all get out. Apparently the game doesn't allow for hybrids, and it's not supposed to be able to happen. (Is what they say) Yet they happen all of the time in my game. I have vampire/aliens, alien/spellcasters and spellcaster/vamps and every last one has something wrong with them. I'd assume alien/mermaid would be the same. They're all especially buggy in CAS and won't remember clothes you set etc. That's probably what you have here. :/