It will be a strange game where players allow this to happen...
Well it often happens, and i find it's a very interesting part of the game.
This happens with the king election too, and it's even more often !
Players forget to think about king election, and try to make all their mal nobles bishops, then the king election comes, and there is only 1 titled mal noble without religious title !
If the player have sufficient support (at least 3 voices with 1 cardinal or 2 bishops), he is elected king.