Checking Godot's source to confirm suspicion about AStarGrid2D

This is interesting and I think you should make an issue if you have the time. I have a completely different use-case in my point and click game, where sometimes if you dig the player into getting themself stuck, they still try to walk to the point even though they are standing on a non-navigable tile. This causes them to jitter back and forth endlessly until you unstick them. I was stumped on why this happened but I think this answers it!