I've also had a few occasions where it'll light and run during priming (no glow ignitor.

One time when I was breaking in a new one, I had primed it and it had stopped near TDC. The ignitor cord was connected but not turned on. When I pressed the buttontp turn on the ignitor it lit and stayed running (didn't flip the prop).

I've even had a YS 4-stroke light without glow.

Makes you think twice before casually flipping a prop on an unrestrained model!