Bulbapedia says that a female Pokemon with a hidden ability has a 60% chance to pass it on without help from an item in Gen V and an 80% chance in Gen VI.
So I'm breeding the Pancham I got in a trade to try and get one with better stats, but I'm noticing that its hidden ability - Scrappy - isn't being passed down at all. Is this a bug? If it isn't, is there a way around it?