I don't think you can re-join but you can always reload the game from an auto-save.

Or none.

I cannot hide my amusement over the fact that running the good old XP seems to have a stabilizing effect^^.

Whatever causes it, I think that we can all agree it's annoying and it's becomming much more common on ICO.  I definitely think that a patch should be made so that you can re-enter a game after you've MD, but it may have to include a whole multiplayer setup change, which would take some time to program.  Hopefully the new patch will help solve some of the issues.