Coherent: Mouse clipping before edge of window

[Mehuge]

The ScenarioButton UI butts right up to the right edge of the screen. It uses mouse events (click, over and out) to open the menu / show tooltips, however the mouse events appear to be clipped (blocked) near the right edge of the window (about 10px or so).

I can't see anything obvious on the html side (no overlapping divs) so wondered if it could be something between the client and coherent.

Could it be something to do with the scrollbar area of the window? It looks like the area that does not respond to the mouse is about the size (width) of a windows scrollbar.