Comment 3 for bug 943456

This appears to be a Unity bug. Gnome terminal is correctly receiving the Alt+F2 keystroke because Unity has told compiz that it has not consumed the keystroke (returning false):

bool UnityScreen::executeCommand(CompAction* action,
                                 CompAction::State state,
                                 CompOption::Vector& options)
{
  SendExecuteCommand();
  return false;
}

So the terminal will receive the Alt+F2 escape code which is ^[O1;3Q
Gnome terminal at least, does not understand such Alt escape codes in the terminal. So it consumes the standard part of the input up to the semicolon (^[O1), and outputs the rest (;3Q) as regular text.

This bug should be fixed simply by changing UnityScreen::executeCommand to return true. That tells compiz that the key combination should not be passed to the app.

The fact that this bug was never visible before seems to have been a bug in compiz-core, which is obviously now fixed.