Hi. Running 2x on Mac 10.5. I have 3 tracks. I split, ( edit, clips, split) a section in track 2 into a single clip and then copy and paste into track 3 (empty space). This is successful, but corresponding area on track 1 disappears! What is going on here? 
Select the track you want to work on by clicking above the MUTE button? It sounds like you had both tracks selected by accident, maybe?
Koz