I think there is a simple bug when playing notes near the border. The notes from the MIDI file are displayed correctly but when I press them on a midi keyboard they are displayed on the left hand track.
The software recognizes them correctly, they're just displayed in the wrong track.
A screenshot follows:
It's not a problem at all and you really did a great job and wrote an awesome piece of software that's very useful for learning the piano.
Looking at the screen shot PB is waiting for you to press A in the left hand because that note is orange. That is why the notes you are playing are being shown in the left hand. You have already played the A C and E in the right hand. You only get one chance to press these notes together. the notes then turn red or blue and then you have to move onto the next note which is in the left hand.
Hope that helps. if this really is a bug please repost.