I have a spline in a 3D sketch. I am trying to move the end and control points by clicking and dragging. After I move a point a small distance, it snaps (to something I cannot see) and I cannot move it any further until I release, click and drag - another small distance - again. When trying to move these points I have to click and drag several times to move it any significant distance, and that is still not really where I want it to go.

I cannot see any settings which would obviously control this. Any suggestions?