I wasn't able to find any documentation of this problem on the forums. If this has been addressed before, then I apologize.
Currently, I'm using Opera Stable version 24 on Windows 8.1 64-bit. Everything works as is expect for tabs and windows. I can create tabs on a particular window, but if I attempt to drag a tab to another window, it will not join the tab bar and become a part of the second window. The second window completely ignores it, and instead, the dragged tab makes a new window. Trying to drag the tab to the window it once was a part of also does not work. Strangely, Opera on Windows 7 64-bit on my laptop does not have this problem.
Has anyone else encountered this bug? I've been dealing with it since version 22 or so, and switching from stable to beta or developer does not fix it.