Its partly a problem, partly a suggestion.
There is missing something when it comes to how to Wish list works when you get a pet on it. When you get a wish list pet in a trade, it will be on the top of the wish list when you view it, easy it remove once its gained.
This however doesn't apply for wish list pets that you get from a growing pet.
Since you can get an new edition of an old pet in the december advents gifts, its possible to get a wish list pet before its grown. But if it grows up to be one of your wish list pets, it doesn't show in the top of the wish list. You have to go find it manually (and that can be difficult if the list is long!)