I installed Opera 26 Beta and so far it does not show that pop-up panel at the bottom.
Well, as I said, that fresh install wasn't really fresh. Now, to be honest, I have no idea where does Opera save its config and data files, cause I'm pretty sure that's what's causing you these issues. Not sure why you didn't go for the Developer version. It's absolutely nothing wrong with it. For what it's worth, it's better than any other Opera version. Anyway, your issue is not related to opera. It's related to the messed up config files on your computer. And now that you installed another version, you know that's true.
By the way, nice wallpaper. What is it?