1. Open emacs and do some editing
2. Alt-Tab to switch to terminator or gnome-terminal
3. keyboard input lost in terminator or gnome-terminal
4. to get it back in terminator or gnome-terminal, I have to
  a. right click terminator or gnome-terminal or
  b. Alt-Tab switch to other application and then switch back

I only find this problem with emacs and terminator or gnome-terminal.
Alt-Tab from emacs to other apps like firefox works ok.
Alt-Tab from other apps to terminator or gnome-terminal works ok.

It seems to me that emacs holds the keyboard input focus and doesnot
wish to give it to terminator or gnome-terminal when Alt-Tab.