Ghirahim is apparently a buggy boss as well. Here's a
strange glitch in the Ghirahim 1 fight that ultimately results in the Wii locking up. And here's
a glitch in the Ghirahim 3 fight where he just disappears after the final hit.
The first video had nothing to do with the game, it was the controllers that messed up.
When my friend was visiting me and playing skyward sword, something similar happened to him.
The nunchuck locked in the position he was holding so he kept moving without being able to do anything about it, and the wii remote itself was not responding, so he could not attack.
It was like the controllers had locked up.
It worked after he reconnected the controller though.
The second one is interesting though, that could be a real gamebreaker, and it happens at the very end of the game.
It looks like he did the finishing attack while the boss was teleporting. Like, he dies when he isn't present, that could easily mess things up.
It's just a theory though.
And if that is the case, then it could happen to anyone at any time.