Need help with SD 3 layering issue

I put this on the Producer 8.5 page but wanted to try here too. In following to a T the Master Class on creating a drum track, one thing is not happened for me the way it does on his tutorial. In creating a step sequencer pattern for ride and ride-bell - when I try to drag that part (which "overlays itself on the first track layer - sequence) down to the 3rd layer, it goes, but leaves a gap in the 1st layer where it was!! On the video, that first layer just automatically fiills itself in......- what am I doing wrong??

How simple - I don't recall that ever being mentioned at the start of the tutorial. I finally was able to force it by locking the clips in layers one and two - then unlock them after I dragged the third sequence to the third layer.....hassle. This is great thanks - I was beginning to wonder if anyone knew.