Extra bar on display of detached audio clips.

I'm a relative beginner working through a tutorial. I've noticed that detached audio clips sometimes get an additional thin bar and I can't find any documentation on what the purpose of this might be. In the first attached image (the "before"), the top and bottom audio clips were originally components of the same video clip (i.e. both a7S3_00189, although the top label is truncated). I'm  about to delete the bottom one. When I do, I get the second attached image (the "after"). The new thin bar seems redundant, as I can just click on the audio clip to select it. Also, the programmer who implemented this feature went to the trouble of making the thin bar the same width as the clip I have just deleted. That's quite puzzling.