Got a bit crazy about correct context sensitive mouse cursors in GIMP's tools during the last two days.
After adding "Zoom in" and "Zoom out" cursors to the magnify tool (which is not really a bugfix), I found that the "Intelligent Scissors" were displaying totally nonsense cursors and fixed the tool (and yes, this is a bugfix :-).
The remaining problem is that many tools still need a mouse motion before they update their cursors. Immediate cursor updates however give much better feedback (it simply feels natural, i.e. "how expected", if the cursor changes as soon as e.g. a modifier key was pressed).
I think I'll look at the other tools as well...