Comment 8 for bug 1500912

I found the cause :

im_context.focus_in ();

On controller.vala line 55 the very specific instruction "im_context.focus_in ();"
 // Input Method Fix
if (this.view is Gtk.Window) //this has to be true, otherwise im_context will not work well
{
  Gtk.Window v = this.view as Gtk.Window;

  message ("Using %s input method.", im_context.get_context_id ());

  v.focus_in_event.connect (() => {
    im_context.reset ();
    im_context.focus_in ();
    return false;
  });

  v.focus_out_event.connect (() => {
    im_context.focus_out ();
    return false;
  });

I'm not sure what this is doing.