Came across this little bug today. Love being able to disable MIDI tracks. The problem is when you re/enable them, they lose their output MIDI port assignment and default to the first port of the assigned VSTi.
ie:
setup a multitimbral VSTi that accepts MIDI from more than just 1 port (VEPRO).
assign a midi track to VEPro->MIDI In 5->Channel 3
Disable and Enable
The MIDI track will have changed output to VEPro->MIDI In 1->Channel 3