"Delete and close gap" stopped working

Question

Another first: In one project, but not in others, "Delete and close gap" will only work if I delete complete clips. If I try to trim a clip, either in the Timeline, or in the Sceneline by trimming in-points or out-points in the mini-timeline under the Monitor screen, a gap created by trimming a scene does not close up.
Stranger still -- Trying another approach to trimming a particular clip, I split it, then tried to delete one of the two new clips using "Delete and close gap. It deleted the new clip but did not close the gap. The action created a black clip image in the Sceneline where the deleted clip had bin, and this new black clip image could not be deleted.
In the Timeline, it is possible to drag the following scenes over to close the newly-created gap, but it's time-consuming. It's a drag, so to speak.
I'm almost done editing the project in question and can complete it without solving this problem, but if I suffered a similar loss of the ability to trim clips in a longer project without creating gaps in the clip sequence, or if "Delete and close gap" failed to work on split clips, I would very much want to know why, and how to restore the lost ability.
Has anyone experienced anything similar?
John B

Answer 1

Thanks, Robert -- You nailed it on your first guess. In this project, for the first time ever, I dragged an audio track to the Narration track. I know it's intended for narration that's recorded directly into PE, but I thought I'd see if I could use it as an extra track.
Also in this project, I've split the audio on the Soundtrack so it's non-continuous, with gaps in it, because I only need it in certain places. From your 2nd message, it's possible this could also be a/the cause of the problem.
I'll keep a close eye on my use of these tracks. In other projects, I have imported audio into the Soundtrack track without causing this problem, but those were continuous music tracks with no gaps.
Another lesson learned.
Thanks!
John B