I have got weird problem with Ambiance (it happened suddenly, no changes made by me): Title bar in all apps can't be set to Ambiance, it simply doesn't change. Does anybody meet such problem?
I would try, using an advanced editor such as MyUnity, and change the theme to something else such as Radiance then change it back, looks to me like its stuck on clearlooks or something. I've had trouble occasionally with my theme not "updating the windows" If you do not have MyUnity installed you can install it from the software center or run this code in the terminal:
Then run the program by searching Myunity in the dash. Then move to the "Themes" tab and select any them other then Ambiance, then wait for it to update then select your final them which in your case is Ambiance. Then log out and back in and it should be fixed.