Anything else installed which changes how windows are positioned, moves them around or between monitors, makes them on-top or similar? It's usually something like that which causes similar problems.
(I mentioned AWM since it came up in an almost identical thread a few days ago: DO Window active after double-clicking video (Actual Window Manager) )
Another possibility is system-wide hotkeys in Opus have been configured which are being triggered by accident. If you've edited your hotkeys and created them as system-wide ones by mistake then pushing the same keys in other programs could activate Opus. This includes hotkeys on floating toolbars (ones that are separate windows, not part of any lister window).