This is an illusive problem for me...it doesn't do it all the time, but often if I for example split a clip(s) and drag or nudge one way or the other, the remaining clips in the direction I drag disappear.  Is there a setting I'm inadvertently hitting (or not)?
 
Thanks.
 
Dave Ayers

What's your record setting? It should be " Blend" instead of "overwrite" if the clips overlap.

I think Kalle nailed it.

This may help. I've notices this as well when dragging clips. What I found is that you must make sure of the selected region in the timeline. If the selected region is further than the clip you want to drag, the other clips will disappear. Make sure only the selected region in the timeline is the amount of the clip you're dragging.