Forgive me if this has come up before, I'm struggling to describe it so I'm not having any luck with searching previous questions. Recently on 10.4.9, when I move my cursor over the timeline, the red straight line gets a shadow. Then when I click to make a cut, the cut can appear where the line is, but more often at the edge of this shadow. Is this a setting that I've accidentally triggered? It's bewildering me and I'd be so grateful for any advice on how to switch it off. Here's a screengrab which might be easier to understand than my ropey description.