Found another one....
If you are using the arrow keys to push a control point on the curve around...
and you push it too far and the curve turns red, the arrow keys are disabled until you click on the point again. If you move it and the curve is still red, it disables again and you have to re-click a third time.
I found it kind of annoying since the point I wanted to move was very close to another and I just wanted to tweak it a bit. Highly repeatable on my install...
Greg