I am using a Raspberry Pi 3 with mt32pi (https://github.com/dwhinham/mt32-pi)

This works well in the follow configurations:
PI -> USB to Serial -> 0-Modem -> DOS PC (COM1) (Using either SoftMPU or SBEMU) -> Monkey Island / Doom
PI -> USB to Midi [M-Audio MidiSport 1x1] -> USB to Midi [DOREMidi] -> Windows Netbook -> (ScummVM)
PI -> USB to Serial -> 0-Modem -> USB To Serial -> Windows Netbook (HairMidi) -> ScummVM

However with these scenario's I get an Unexpected midi status on my PiMT32 LCD:
(Resulting in wrong instruments, notes not off etc).
PI -> USB to Midi [M-Audio MidiSport 1x1] -> DB15Midi (SerdaShop) -> ESS-Solo-1 -> DOS PC -> Monkey Island / Doom
PI -> USB to Midi [M-Audio MidiSport 1x1] -> DB15Midi (SerdaShop) -> CMI8778 -> DOS PC -> Monkey Island / Doom
PI -> USB to Midi [DOREMidi]-> DB15Midi (SerdaShop) -> ESS-Solo-1 -> DOS PC -> Monkey Island / Doom
PI -> USB to Midi [DOREMidi]-> DB15Midi (SerdaShop) -> CMI8778 -> DOS PC -> Monkey Island / Doom

I am trying to understand the source of the issue; any suggestions?
Would this be a speed issue (tried disabling cache, no difference)? PSU issue; do I need to connect ground from PI to my DOS PC PSU Ground?