That is a note off screen. You'd have to scroll down to see it. How it would be placed there is beyond me, though. Here the insert key is assigned to 'insert note at mouse cursor', I wouldn't expect it to insert below the shown area, so this seems to be a glitch. I couldn't recreate it here.
Thanks again! I've produced it while trying to insert a program/bank select event in this lower area with the insert key. By the way, all notes which are scrolled down below the notes window reside on this lane and wait there to be scrolled up again :D (just noticed that)
Yep, that is a very nice feature. Of course the same works for notes that are scrolled up. I was now able to recreate the insertion when hovering the mouse over a controller lane and hitting the insert key. Definitely a bugletto.