You end up with this:

Yep. That's two Hati there. Both of them fully functional.
Essentially, trying to summon the pet from your stable gives you the alert that it's dead, but Hati still pops out. Then when you res it, boom. Second Hati!
Summoning a different pet will change it to one Hati again, as will unsummoning and resummoning your pet. But it's worth the double-take!
I already reported this bug, because the abuse factor is far too easy, but it doesn't mean that I didn't want to show at least one picture of an Ultimate Beast Master.
.... at least, 'Ultimate' unless someone manages to summon more than two Hatis.