I would agree. it’s not just working if you use it for tidying up dodgy midi setups. What I cannot understand is that in my setup (midisport 4x4) that every midi input and output is listed twice, once as DirectMusic and once as Windows MIDI. (Any idea which ones to disable / prefer). It can also happen if I have more than one out channel enabled on my mp5 master keyboard.
That rears its head once in a while and creates duplicate nots, the only way I can currently delete them is by using the arrow cursor and then hit delete on every second note. Hardly a professional way of dealing with duplicates but of course the “delete duplicates” function does not deal with this at all.