I would love for that test to be double-checked if possible. Move the original qwindows.dll completely out of the platforms folder, and put the new one in. The new qwindows.dll file should be the only file in the platform folder. Also make sure your launching the version of Sigil that has the new dll (in case you have two Sigil installations and are accidentally launching the wrong one). Also make sure to delete the existing debug log before launching Sigil.
I ask only because I got different output (with SOME name appended to my serial number) when testing the new patched dll. I never made any registry changes and still saw different results.
I first renamed my existing dll and left it in the platform folder. But after I named them back, the patched version of the dll was still being use (even though it had the wrong name). That's why I'm recommending only the one dll in that platforms folder. Windows has the annoying habit of sometimes using routines from dlls still in memory rather than accessing the dll again.
EDIT: We cross-posted, obviously.
Thanks for your diligence.
Thanks in advance.