The issue has been identified. The change in the Creators Update affects how Windows 10 treats unmanaged .net code. At the time I was told this, about a week after the release of the V1709 update, development was still early in the investigation phase. At the time, it was not clear whether the core issue was a defect in our code, or whether the change in the creators update corrected a defect in Windows for which we were previously working around. At the time, it was also clear from the investigation that the fix would require extensive work.

It is a top priority. It is the current hope to include it in 2018.2, but because the fix requires so much extensive work, it is still too early to say that it definitely will be.

Point of curiosity: Why isn't this a problem for Sage 50 2017/18 CA?  Is it not also written with unmanaged .Net?  I also haven't seen this problem with any other program that I run or even know of, so it's quite curious indeed.

Point of curiosity: Why isn't this a problem for Sage 50 2017/18 CA?  Is it not also written with unmanaged .Net?  I also haven't seen this problem with any other program that I run or even know of, so it's quite curious indeed.

To my knowledge, it is not, but that would be better posed under the Canadian forums if you really want to know. Even though the branding is Sage, the Sage 50 Canadian version and the US versions were completely separate software companies acquired by the Sage Group PLC years ago. They were Simply Accounting and Peachtree Accounting, respectively, and were both rebranded as Sage 50 sometime in 2012. Even though both companies have been under the Sage umbrella for years, largely development was still independent, so it's not so curious that the codebases are still completely different.

Right, that makes perfect sense. I had forgotten about the different lineages. Maybe one day they'll be united, but definitely not quite yet. It's a bit unlucky though even one of them has the problem (the CA version definitely doesn't), since I'm pretty plugged into program incompatibilities with Windows and haven't seen this kind of issue in quite a while.