Disappearing midi clip

[madlab]

I was working in arrangement in Live 4.1 on my pbook on a session with about 10 Mono audio tracks, a few native gates, EQ4s with one or two bands active, 2 CompII and 1 Filter delay. Then I opened an instance of Stylus classic on a midi track and dragged the clip. I was playing around and the clip suddenly disappeared and stopped playing. There was no way to cancel this and I'm sure I didn't delete it by myself in any way. I reimported it and it worked OK.