Windows 10 64 bit - it's still an issue for me. When I set the default program for opening .jpg for instance to Paint.net, thumbnails are not created. When I change that to paint or any other photoviewer, the tumbnails are created and are visible for Paint.net.
But when a new file is created with Paint.net as default, no thumbnail is created. Is there a way to roll back or fix?
In the attached picture you see what I mean. In Explorer, the left picture is the thumbnail created when "windows paint" was set as default for .JPG.
At the right, the same picture (made a small change with Paint.net) when Paint.NET was set as the default program.
I hope this is clear.
Thanks for the good work