Group By Modal View

I have set up 25 Group By rules in a grid but when I click on the Group By button, the modal window opens but will not show all 25 radio buttons and shows no scroll bars unless I zoom out (CNTL + Scroll Wheel). Only then does the scroll bar appear and the full selection.

What’s the magic to force the scroll bar and also have the Group By window appear as I need it?

Thanks - Ken