When you click a note, its still visible but when you play the song itt gets deleted.
The other glitch is that I put a drum in Layer 4, (it was top of a bass, layer 1) and I clicked the drum (still was in layer 4) and changed it to whole, then the bass in Layer 1 did those settings and the drum was eighth!
Play-and-pause is the most convenient solution to the first problem. You can more learn this problem here (problem #2).
Unfortunately, I don’t know much about your second problem. I’ve encountered before on rare occasions. My suggestion would be to restart Notessimo (don’t forget to save before doing so).
That first one is annoying as crap 
But you basically just have to change sheets really quick. That normally seems to fix bugs for me. That or copying the sheet to another sheet and copying it back.
i don’t have that problem