Super Champagne is indeed lethal so are a few other combinations, see this http://www.owalreptiles.com/issues.php for details.
Many people are not that knowledgeable when it comes to genetics let alone with potential issues when it comes to specific mutations. And some people will say ANYTHING to make a sale, years ago someone wanted to trade me 1.2 desert for some enchis and they told me their desert would lay eggs. (it was early but already known they would not)