Oh yes thats a great answer.
No the Problem is a bit different.
Lets make an example.
Imagine, open windows: Opera and File Explorer from the OS.
Then you are in Opera. Press Alt+Tab to change to Opera. Opera keeps staying in front, and the Window look changes to inactive. In the Taskbar the file explorer gets active but does not come to front.
Same problem can be seen with overlapping windows.
I can reproduce the Problem on 3 Windows 8.1 machines.
The Problem keeps with other applications after closing Opera, a reboot fixes this. Problem is back again after Opera beta was started.