I was just watching a UK Championship game and came across a rare incident. Mark Williams potted the yellow after the last red. The referee should have re-spotted the yellow, but he forgot. Then Williams re-spotted the yellow himself and continued his break.
A commentator on BBC said that it was allowed. I checked the WPBSA rules, the balls don't necessarily need to be re-spotted by the referee, so the commentator is right.
I wonder a slightly different case. If a player re-spots the ball just because of moving quicker than the referee, is it allowed as well? I don't see an explicit rule prohibiting this, but it can prevent a proper game. Maybe such a case has happened before.