Comment 2 for bug 845653

A workaround is to open System Settings and click Keyboard. Switch to the Shortcuts tab and select System. Change "Show the run command prompt" to Alt+F2.

Launchers>Launch Terminal should also be Ctrl+Alt+T. I don't know why these two settings aren't pre-configured properly; I've actually spent a good amount of time trying to understand what's broken but I haven't been able to figure it out.