I created this one, which is similar enough to yours that it should work:
#EXTM3U
1\1234.mp3
1\2\Reaction.mp3
Neither song shows up - the playlist is listed as empty. There is obviously a bug in the m3u parser somewhere, although the fact it works for some people (well, at least drlucky) and not others seems bizarre.
The Fuze+ also seems to store a copy of the parsed m3u data somewhere else, because I noticed I edited an existing m3u file on the player (from a text editor) and the songs listed in that playlist on the Fuze+ interface did not reflect those changes. It only showed the changes if I deleted the m3u file and replaced it.
So is there anyone else besides drlucky that has been successful with this?