I was really hoping this issue would be resolved, but it actually got worse. Not only you can block the entrance, but now if an unaware person enters a cave and the cave is blocked from the inside with a hearth fire, then you can't move neither you can exit the cave. You can either destroy the hearth fire or be forced to recall to your own hearth fire.
In my opinion, hearth fires shouldn't be used like that any more. Their usage was meant to be a way to return to your home, and everything else seems like an exploit to me. Just make them unable to block cave entrances, house entrances etc. or make people able to just walk over them.