Hey there, @GideonWilliams ...

I saw a different thread about this last week some time of people reporting the same issue.  I, too, was able to replicate this in my own sandbox course.  I'd suggest reporting this to Canvas Support so they can log it.  Chances are, they already know about this, so you'd be added to their existing tickets and updated if/when a fix is released.

How do I get help with Canvas as an instructor?

Keep us posted on what Support tells you.  Thanks!