I agree with the folks who say Navi is behaving normally In the dog world, whoever has an item 'owns' it for as long as they have it. When they leave it behind, the next dog that picks it up 'owns' it. So, in Navi's mind, she was protecting her things, not stealing from Maya.
Also, the fact that Navi is baring her teeth, ducking her head and air-snapping are all really, really nice. I know they look ugly, but dogs that give great big warnings are fantastic, because they rarely have to resort to anything worse. Just like you saw, Maya got the hint and moved on.