Trin, thanks for the detailed answers.
I am still having the same problem since the latest update on my Macbook Pro: version 42.0.2393.94. Ever since that update, whenever I choose a bookmark from the top Bookmarks menu or choose anything from History, the selected website does not open in the tab I am currently using. Instead it opens up in a tab on a minimized Opera window. I have 5 Opera windows open, each with various tabs, with 4 windows at a time minimized. When I choose a bookmark or history, it will generally open in the left most minimized window's visible tab, but sometimes it will open in a different tab. Since the update it will never update in the tab I am using.
Avi, let us know how to add pictures, and I can replicate it.