MIDI Export is a bit broken

TLDR: Exporting to MIDI with whole score exports with wrong patches in some instruments. Exporting parts instead reveals split tracks resulting in missing sections in DAW. Fix and options requested. What is RPN?

I'm trying to fully utilize Musescore as a music-making tool, and I'm developing a process whereby I create the sheet music in Musescore, then export it to MIDI and add effects and automation with LMMS. However, there is the small problem that exporting to MIDI doesn't give you an accurate score. I'm not talking about dynamics playback or soundfonts or anything; it literally spits out an incomplete score. For example, see the attached Musescore file and then compare it to the MIDI file. Not only are some of the sounds completely wrong, which is ridiculous since they're all GeneralMidi compatible and whatnot, but several parts are straight-up missing, like the brass synth. Trying to look further, I separated the parts (which worked as intended) and then exported all of those to MIDI. The sounds are correct now, at least, but take a look at the attached brass synth MIDI. If you play it with Windows Media Player, it sometimes plays the part, sometimes not. In LMMS, it imports only the tail end of it. But in MIDI Editor, you can see that the tracks are separated due to the split staff. (This is more apparent in the electric piano part, which is almost entirely composed for the left hand.) This means I'd have to put it all in one staff in order to edit it in LMMS - a tall order if you account for more than two voices per staff. I understand the need to split the tracks, but it would be nice to have the option to export all split staffs as one MIDI track.
That said, I was looking in the preferences in the "Export" tab and saw an option called "Export RPNs." Any explanation on what that is? Couldn't find it in the manual.

Edit: Weird. Although the bass synth is all in the left hand, it exports as one track and is detected as such by LMMS. This means that either Musescore detects that there's no RH and puts it all in Track 0 or LMMS detects that there's only one track and uses Track 1 instead.