Since about 20 months after start, a solution for Bug#12713 finally reached the main tree.
If you’re not using stored functions this may have a very little effect on you, since other than fixing the problem at hand it was no more than a cleanup of the execution flow and the server/storage engine interaction. Anyway, it was a difficult one, one out of a dozen of design gotchas we added to the server with 5.0. The all-time record for that sort of difficult bugs
is Bug#989, reported back in 2003 and planned for a fix in 6.0 only.