MIDI step input - grey notes

When I try to do a step MIDI input in my current project, it makes the notes, but they are all grey and don’t play and disappear when I try to playback. Strangely, when I then input more notes via my keyboard, they reappear and my new notes are added. But then I playback and–again–no sound and the notes disappear from view.

What’s going on?

Are those notes being inserted outside the Part’s boundaries?