Drag a sample into the song editor, like piano02.ogg, assign it to a midi input
go into the piano roll, record something by using your midi device for input
close out of the piano roll, delete what you just recorded from the song editor, re-record from the piano roll, repeat several times
every time you record again, the volume seems to double
deleting the sample from the song editor and re-inserting clears it out
only happens when you record with a midi device, if you draw the notes out in the piano roll, it's fine.