Minor pedantry comment on the PR. Also I expect you've confirmed that this doesn't pop up a window when you're building?

No, it actually still does, I can't really think of a way around that! This way though, unless the user happens to have their beloved images in frame 731 and 732, their work will survive building afw, whereas without these changes, any images in frame numbers 0 and 1 get blanked out.

Ah I see! There are two problems. One is the annoyance of a window popping up, and the other is the catastrophe of having the build kill a window that you're working on. And this fixes the catastrophe. Great!

Yes, exactly. I can't really see a way around the other, except for not having ds9 open in the first place. Given that it only pops up if you already have it open, it's really not so bad - can feel a bit like there's a ghost in your machine, but given that most people who are building afw are reasonably towards the pro end, I think that's not so bad.