Icon corruption using transparent PNG files

In bringing a project to Windows, I see that the app icon is corrupted (32bit, so not THAT issue). When I select the App -> Icon editor, the PNGs that I drop are not being handled properly and the transparent portions are turning up black. Checking the Mask elements shows blank entries.

The PNG files do show up as transparent in Explorer and the Windows image viewer.

Bug, or issue with PNGs on Windows?

Xojo 17r1.1
Windows 10

I’ve discovered that by dropping the PNG files onto the “Preview” page, it works as expected.