Dragging automation nodes to the correct level

I created a track and recorded audio. I added a volume automation lane, created and dragged nodes. Everything seemed to work as expected. As was editing the automation, I accidentally set the volume above 0.0 db but dragging it back to zero fixed that. Easy!
 
Then I wanted to loop that particular clip so I copied and pasted it after the original clip. When I went to add volume automation nodes I was struggling to get the lines to stay at 0.0 db. As I was dragging the node, the little tool tip like popup showed that I was at 0.0 but as soon as I let go it snaps to 1.4 db. I tried this quite a few times and each time it said it was at 0.0 db but when I let go, it snapped to 1.4 db.
 
Finally, I just moved the node to below 0.0 db then let go and it snapped to 0.0 db. I must be doing something wrong?
 
I read through the docs about automation and it makes it sound easy. I did notice that I could have hit ctrl then dragged and it should have snapped to a previous node. That may have been easier. But what was I doing wrong or just misunderstanding?
 
Thanks