...and now the Visio file
Fixed the problem. It was poor translation of custom fill patterns when saving the V2007 file to the V2019 format. The cure was to rebuild the patterns from scratch. Then, everything behaved properly. For those interested, here's the working VSTM file.
Nice find, how much are you expecting from your Microsoft bug bounty? ::)
I've just checked all the shapes I've created with custom fill patterns and they all seem ok.
Just a small, hand-made basket.
Well, this is interesting. Went back to the translated file, and, not only was there the fill pattern problem, but also the grouped shape that uses the fill pattern. So, tried several earlier versions of the V2007 file, and all exhibited this behavior.
Today, I looked at the landscape version of this photoframe template. It translated just fine. No issues. At this point, I'm guessing there was an early corruption that didn't impact V2007, but does when converted to newer format, and that it had propagated into each updated file. Other than that, no clue.