I recently upgraded from Kubuntu version 12.10 to 13.04 using the automated tool, only to find several display related problems. The system had not been upgraded from an earlier version before.
First of all, most semi-transparent dialogs such as the battery dialog displays in a flawed and often unreadable way.
This includes the login dialog and the volume level bar that is shown when the volume level is changed. Some (such as the run dialog (Alt+F2) and the thumbnails shown when hovering over windows in the taskbar) do show correctly, however.
Secondly, I have noticed that the Present Windows effect will lead to windows flickering while the effect is visible.
I run an integrated Intel graphics card on a laptop (Thinkpad E320) with stock graphics drivers. I can't think of any system modifications that could have caused this., as the installation I have is mostly standard.
None of these problems existed before the upgrade.