When pinning Notepad2 to the taskbar in Windows 10, a duplicate icon is created. Unpinning the duplicate also removes the original icon, leaving you always with two icons on the taskbar.

To resolve, look for and remove the following line (located in the section [Settings2]) from the settings file %APPDATA\Notepad2.ini:

ShellAppUserModelID=Notepad2

Save the file, then unpin and re-pin Notepad2 to the taskbar.