It sounds dangerous. You want to be able to extend a clip over other clips? Hmmm. Like I said, it sounds dangerous.
I generally have all of the clip audio in audio track one. Added audio (like music or voiceovers) in track two. And any other audio, like modified clip audio, down in track three. I usually turn off track one audio. So if the audio is not copied down to track three, the clip audio is not in the way in the first place.
So I guess I never noticed that it could or could not be done your way.
Steven
Adobe Premiere Pro 1.5 / After Effects 6.5 Pro https://www.stevengotz.com
Learning Adobe Premiere Pro 1.5 https://www.lynda.com
Contributing Writer, PeachPit Press, Visual QuickPro Guide, Premiere Pro 1.5