Why different button indexes onMouseUp and onMouseDown

[Todilo]

I want to know when middle-mouse and right-click are released. I track them onMouse fine but in order to get when they are "up" I use:

   useGesture(
        {
            onMove: (state) => onMove(state),
            onMouseDown:(state) => onMouseDown(state),
            onMouseUp:(state) => onMouseUp(state)
        },
        {
         .....
        }
    );

It works fine, sort of, but I get different numbers on button pressed.

onMouseDown:
MiddleMouse
state.event.button = 1
state.event.buttons = 4

RightMouse
state.event.button = 2
state.event.buttons = 2

This is consistent with onMove.
However
onMouseUp
MiddleMouse
state.event.button = 1
state.event.buttons = 0

RightMouse
state.event.button = 2
state.event.buttons = 0