In all browsers (including Opera) and all other programs having a scroll bar, the right side of the GUI is reserved for the scroll bar. This allows the user to simply move the mouse to the far right very fast, knowing that it will land on nothing but the scroll bar. The scroll bar is on the far right side. There is nothing after it. So the user can move the mouse without checking where it is.
In the latest version of Opera, this has been disrupted. Now, there is this very thin column on the right side of the scroll bar.
This narrow interface column is totally useless and serves no purpose (other than to make the user crazy).
Now, every time the user moves the mouse to the right end of the interface, she will actually land it on that narrow column, instead of the scroll bar. And thinking that it is on the scroll bar, she will try to drag the scroll bar up or down. Now, every time she drags it (to relocate the scroll bar), it is the whole interface that gets re-positioned. Very ridiculous and counter-intuitive design. Sometimes, the webpage stops working and gets frozen by this dragging. I need to duplicate the tab and continue on the new tab.
This reminds me of the new design of Gmail, where such a narrow and ridiculous column exists after the scroll bar (on its right).