This update should remove the interference between the two play buttons in exercise and MIDI player controls. And it will work on the latest one. Like if our exercise was working and now we open a .mid file, now only the MIDI player controls will work, and pressing the play exercise button won't have any effect. Similarly, if the midi file is playing and we request for a new exercise, the midi player will be turned off (timer to 0) and the exercise will play. Now the MIDI player play button won't work. Before creating a new exercise, I have stopped the midi player first and then cleared the old Song object for midi before creating a new song object.

Open any exercise, you should only be able to play it using the play question button, and the play button in MIDI player control shouldn't do anything.
Open a .mid file and play it (it is the current Song object now). Now try to use the play button from exercise panel (that was already open), which shouldn't have any effect on the .mid playing.
Now open another exercise (it is the current song); it should stop the .mid playing, return the timer to 0, and play exercise music.