I just started running into a problem a week ago. I can't change the theme for Ubuntu without restarting the computer. This includes the GTK theme, the window decoration theme, and the icon theme. If I completely restart the computer (logging out doesn't work), the theme updates. However, I'm only able to set it to either Ambiance or Radiance. Any custom themes don't work.
I've tried removing Unity Tweak Tool and installing it directly from the Ubuntu Software Center. I've also tried setting the theme using gsettings, but it doesn't have any effect.
Does anyone have any idea what's going on? Thanks a lot!