It's really horrible I must say. I sometimes have geometry issues and then try to go one by one through them and fix these cases. Therefore I mark the area points and delete them for instance. After that I doubleclick the line to create a new point. And now I often have the issue that by dragging this point I create a green circle at that position instead of just moving the point.
I would like to know why I often cannot move it and am getting these green circles instead. Also, if this is a feature, what are the green circles good for, I was thinking that sign is showing duplicated points? And the last question is, why does the point movement sometimes work, but in 80% of cases it does not?
Here a picture to make my issue a bit clearer: