Copy sound bug or feature?

Today I found something interesting. I wanted to copy track 1 to track 2 (sequencer data + sounds). (to get stereo out of 2 almost identical tracks panned left/ right)
all the copy commands etc we done while playing. I realised that the track became muted although no mute was active. it needed me to push on button 1 and 2 to get the tracks alive again… strange …