Hi
"I have 3 clips A-B-C on video track 1 and a sound file on audio track 2.
I drag and drop to rearrange the sequence to be A-C-B.
Result: where C is inserted audio track 2 will be split and the second half shifted back so that it still matches with the former position on Clip B."
Exactly! ...And this is despite Audio track 2 being "independant" One would expect it to stay where it was and remain unchanged.
However, having set up this combination of ABC on the timeline and a soundtrack on Audio 2...
Switch into Storyboard Mode.
Now drag clip C so that it is before Clip B and drop it there....a green bar appears betweeen the thumbnails to show where to drop it. The order is now ACB.
On switching back to Timeline Mode you should see that Audio track 2 has remained in place and unsplit and clip C is now positioned in front of Clip B
Storyboard mode only acts on video track 1 and its sound files.
Nat