the user of the issue you are referring to, has a registry entry with missing quotes (") in the shell open command, which is a leftover from an older installation that had this bug.
currently there is no other known way than to call “notepad++.exe” “%1”, if there is a space in the path.
the full path, with possible spaces, has to be in quotes, to be passed as a single argv, otherwise every space would trigger the rest to be part of a second, third, etc. argv.
you will need to recompile your app using your path/file argv (single argv) in escaped quotes, usually written like "\"path to your\\file.php\""