Were you using Box Sync on your user profile/settings folder?
Opus windows don't open themselves so something must be making them open, but I'm running out of ideas as to what it could be (as long as unclosed windows are not just accumulating in openlisters.oll and never being closed).
If you could create a Process Monitor log of what happens while the windows are being opened (being sure that it's not just old, unclosed windows stored in openlisters.oll being loaded), we might be able to see what's happening from that. If you do that please let us know which folder the windows were opening for during the logging period.