What I want is to be able to somehow differentiate opening bags of a specific pet with a hotkey, instead of both simultaneously. Super annoying when GY farming with horse and bear and one of their bags get full you cant just bind a key to open only one of em, and chances are the full one will take preference, also preventing you from right clicking to load the pet up.
I guess it could be easily fixed by the game checking all open pet pags and assigning the items to one of the free ones if the top-most open bag is already at full capacity. Of course with 3 or more pets with bags this would need to result into a randomized placing, but it hardly matters to the player and would remove the need to manually close the extra windows.
Edit: This could be solved by using a multikey bind, e.g. V+1-9 to open bags of the pet in a specific slot, and these the player could order around in the pet screen.