Well, we didn't get the hole fixed because we knew we were getting a shower installed later. OK, so it was a year later before we finally got around to it, but that's not the point.
Anyway, the shower is now in place, and when we switch it on ... well, sometimes it's perfectly fine, but other times we get this seconds later:
Ha! I knew it was a good idea to spend an entire year with a huge hole in the ceiling of our living room! We wouldn't have spotted the problem otherwise.
Until the plumber can come fix it, we now have two showers: one upstairs, and one downstairs directly below it.