This is total hearsay and guessing, but since you've also got nothing I figure it's worth mentioning - I had gone through the entire tutorial and also messed around a little with the scenario editor, but then not saved it, and earlier in the log are some errors about attempting to disconnect signals from non-existent callables, and sometimes connect signals to already-existing callables. They start on line 6493 if you're interested in those. Maybe something was called which was no longer valid, somehow, after all of my opening and closing and reopening of menus and things?