A problem with alert dialogues and moving to other workspace

Hello. I'm observing a problem with Opera where it displays an alert dialogue at the top of the window, I try to click on it, and focus goes to my other workspace. When it does so, there is a shadow near the top of the screen, I guess for where the alert box would have been. I've observed the same problem in other applications. I've tried googling for this but I haven't been able to find a solution, hence my asking here. If anyone can help me solve this, thank you in advance.

Image?

Can you post a screenshot?

I will if I can. It's just that this problem happens at random times.