Hmm, have you all sidebar enabled? This looks like some part of Opera thinks that sidebar is visible and does steal clicks from that area.

If you could make this 100% repeatable (starting from normally working situation), then it would be good idea to send Bug report to Opera team.

Maybe someone will experiment with sidebar, twitter etc? I personally have sidebar completely disabled in my Opera and I don't use twitter (or other such apps) either, thereby no help from me 😞