I'm not sure how to explain this. So see the screenshot.
Not really enough details were given into your setup. If you're running Ubuntu in VirtualBox, then that could be the issue. You could also try installing updates to make sure your graphics card (or any other drivers and software) are up-to-date. If the problem is still prevalent after updating, then try switching to the classic interface. This can be done by going to the login screen (either by logging out or rebooting) then going to the dropdown menu on the bottom of the screen. Change the setting from "Ubuntu" to "Ubuntu Classic" It may not have as much eye-candy. But it'll run a lot faster and be a much smoother experience overall.
Hope I've helped.