Windows 10 and preference clearing.
On Windows 10 when you set preferences of file types it clears out the next time you open it. The preference is still in place on custom. E.G. add .1235 and then close out the Notepad ++ if you go back in preferences it is NOT listed in there but you can click on the file type and open it. It also does not let you remove the custom associated file types once you have associated them unless you reghack it out.