Thanks for the example. I’ve confirmed the tooltip and mouse cursor bug.
The Spinner currently only detects the mouse over its coloured arc. When the rotating gap passes beneath the pointer, the tooltip disappears. This also explains why the centre doesn’t show a tooltip and why an inactive Spinner doesn’t show its tooltip or custom cursor.
I’ll fix this so the whole control responds to the mouse, whether it’s active or inactive. I’ve logged Bug #1759.
I haven’t reproduced the spinner itself disappearing completely. In my tests it keeps rotating while the tooltip appears and disappears.