Hi Bernhard, so now that I dig into it a bit more I see that there is already something in place that is supposed to be routing mouse wheels to the viewport under the mouse.

So I guess the MoI function that retrieves the viewport under the mouse cursor point is not working right on your system.

Is your multi monitor configuration unusual in any way, like is each monitor in some separate coordinate space instead of being all one connected desktop or something like that?

- Michael