Drag and dropping a sequence into a timeline

V25.01, Mac OS Ventura 13.6.4

I'm dragging a sequence from bin browser into an already open timeline - the clips show on the timeline but they're slightly transparent, image attached (dragged sequence darker blue to the right of the timeline indicator). They can't be selected and undoing Control Z doesn't get rid of them. If I close the sequence and reopen they're not there. I feel I'm missing a command but I'm sure this used to be a simple drag and drop. Incidentally, selecting insert/overwrite as nest or individual clips doesn't make any difference, they show up as individual clips, albeit unable to be edited.