Just posting this for further reference.
I started using the Pattern Event editor with Sampler tracks mostly and noticed that, if you switch the Sampler track back to MIDI part, the pattern keeps playing if NO MIDI PART IS PRESENT on the track. If you draw even an empty MIDI part, then the Pattern stops playing.
Not sure if that’s a bug or a quirky expected behavior. I tend to think it’s a bug.
Oh also as you seem to know what’s up, is there away to create new lanes in the Pattern section by midi learning without having to manually input the notes ?