I think there's always an issue once a singer gets their foot in the door and (like a lot of relationships) appears to initially like everything you do, only to find a year or so down the line, their tastes are vastly different and they start changing the set list completely.
If your band has a style, you need to make sure the front person (amd everyone else?) is on board 100% with that kind of music.
Personally I'll play anything within reason and happy to learn an entire new set list in a few weeks for the right band/singer.