Ok thank you! That was the fix. I got my xmax and xmin the wrong way round!
One other piece of feedback about the UI, since we're here on this example. I recorded a short video to show what I wanted to say about the ability to tweak the boxes.
I'm wondering if controlling when the double-arrow resizing is actually in Prodigy's hands at this point; maybe it's just a browser thing. But you can see it's a bit difficult to access the resizing, in any case. Probably in an ideal world what I'd want is for the resizing arrow to be available to me not just at the half-way point and the corners of the rectangle edges, but also along all the lines as well?