As you can see from the screenshot, I'm unable to delete the hymn number from this slide.
As a workaround, I have to add a second hymn number. It's possible to delete that hymn number, and when I do so, both hymn numbers are deleted.
But it's weirder than that. It's possible for me to add the hymn number to the title slide, and not the other slides. But if I do that, any time I make a change on the other slides, then the hymn number will reappear there.
