Vampire X Werewolf Only Produce Werewolf Babies

I've seen a couple of other people post about this, and responses are mainly "you're just unlucky", but that seems a little buggy to me... 

I have a vampire (f) and werewolf (m) couple who have had five children together. ALL five children are werewolves. I was really hoping to play a mixed household, especially since I had about 50% werewolves in my last generation, I was hoping for more vampires this time around.

Perhaps it's also relevant that the children's grandfather was a pack leader, so there are multiple generations of werewolf genes? I know Spellcaster genes get stronger over time. I also tried trying for baby in the coffin, but it still produced a werewolf child. 

I'm going to add a "on a dark ley line" trait to the lot to see if that helps, but has anyone else had this problem with mixing occults? Any tips to overcome it? 

This is my legacy family (7th generation), so I'm really bummed I haven't had the 50% - 50% experience that I was hoping to play.