I have got this 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. How can I solve this problem?
I would try
unity --replace and if nothing changes
I would try using an advanced editor such as MyUnity to change the theme to something else such as Radiance then change it back. Looks to me like it's 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:
sudo apt-get install myunity
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 theme which in your case is Ambiance. Then log out and back in and it should be fixed.