Ahhh, yes I have "Displays have separate Spaces" disabled since I need to ensure the menu bar and dock never pop up, for an exhibition.
This is the other characteristic of exhibitions, the public will find any bug or chink in the armor. :-)
The "Receive Mouse Delta" node doesn't always have 0 on the output even when the mouse is stationary.
The documentation says this can occur when the point is on the edge of the window, but actually can occur when the point is inside the window.
If the node isn't associated with a window the residual value can be as high as 6 pixels.
Anyone have a nice solution to handle this ... haven't found one myself yet.