notes hanging after stopping player (using MIDI instrument)

Hi Guys,
I am evaluating Musescore "development" version. First, let me thank you for making such good software and available for free, i tried others and Musescore remain the best one.

I still have issue when playing music and stopping the play, using midi channels instrument, most of the time it is hanging playing continuous notes.

I have a SY77 from Yamaha and an organ Electone EL90. My computer is connected to SY77 with Midi in and out and SY77 forward the midi IN via midi truth port to my EL90.

Mostly I use MIDI file that I modify to use adequate channel to send the midi to my devices.
If I want to play ... I just need to mute the track i want to play and when I play Musescore, I physically play my instrument in the background. If I need to stop then it is hanging and there is no panic button to reset so I must switch off either my SY77 or EL90.

I have tried different configurations and it is always ending with hanging if i stop the play from Musescore (i don't even need to play myself to make it hang).

So, would it be possible to have a panic button or to change the code in order to “kind of” send an all notes off when you press stop on the player?

MIDI CC 120 All Sound Off Mutes all sounding notes. It does so regardless of release time or sustain. (See MIDI CC 123)
MIDI CC 121 Reset All Controllers It will reset all controllers to their default.
MIDI CC 122 Local On/Off Switch Turns internal connection of a MIDI keyboard/workstation, etc. On or Off. If you use a computer, you will most likely want local control off to avoid notes being played twice. Once locally and twice whent the note is sent back from the computer to your keyboard.
MIDI CC 123 All Notes Off Mutes all sounding notes. Release time will still be maintained, and notes held by sustain will not turn off until sustain pedal is depressed.
MIDI CC 124 Omni Mode Off Sets to “Omni Off” mode.
MIDI CC 125 Omni Mode On Sets to “Omni On” mode.
MIDI CC 126 Mono Mode Sets device mode to Monophonic.
MIDI CC 127 Poly Mode Sets device mode to Polyphonic.