When in EDIT mode (screen) I select nodes and I am sure I used to be able to move them either by dragging them with mouse's LMB held down, or I would move them with the ARROW keys.
Suddenly - which is confusing me - when I press the ARROW keys, the whole screen moves.
I just went to another machine and tried it.
That is what happens.
So the machine on which I am working seems to have decided to change how it interoperates what it does with the ARROW keys being pressed.