I read your message as I was undergoing the same issues with my own computer and I finally found a solution. All you have to do is press on the opera icon on the complete top left of your tab click on it and find the quit button in the options prior to clicking on the icon
I installed Opera today and came across the same bug.
Your solution seems to have fixed it for me, at least for now, however this is not a solution any everyday computer user would think of or even be able to do.
Is this a known issue or does it need to be reported?