If you turn on the notify_debug stuff described in this FAQ, do you see a lot of activity being reported?
(Running Process Monitor might be an easier way to do a quick check. They'll probably show similar information.)
It's a pure guess but maybe there are so many file changes being made that just parsing them to work out if they correspond to a path that Opus is showing is causing a lot of CPU use. Seems unlikely but worth a quick look, perhaps.