Dogs unresponsive after geting in mine cart

I had six dogs that behaved as expected. When I got in a mine cart, road away, left the game, then came back four were missing (maybe to be expected), but the last two were completely unresponsive.

They were sitting, which I did not tell them to do, and they would not respond to any commands. To be clear, they were still exactly were I got on the mine cart, as they did not fallow.

I will try and replicate this again soon.