To reproduce bug:

* open an xterm
* open a gedit window
* Double click the gedit window in order to maximize it
* ALt-Tab to the xterm
* Attempt to grab the xterm by its title bar

Doing so grabs the gedit window rather than the xterm.

I dug around a bit with git bisect. This diff seems to have caused the bug:

$ git diff 9abdc6c0fab7b66380f1f1eb555c89cbc1131e1d 38faa8fe109071dcb9c49fdbc13774d13f4

diff --git a/ChangeLog b/ChangeLog
index 4aaea57..507f42e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-12-19  Thomas Thurman  <tthurman@gnome.org>
+
+       * src/ui/frames.c: when the user double-clicks the title bar,
+         end the grab op.  Closes #401028.
+
 2008-12-16  Thomas Thurman  <tthurman@gnome.org>
 
         * configure.in: Post-release bump to 2.25.89.
diff --git a/src/ui/frames.c b/src/ui/frames.c
index 093af92..700e747 100644
--- a/src/ui/frames.c
+++ b/src/ui/frames.c
@@ -1388,6 +1388,7 @@ meta_frames_button_press_event (GtkWidget      *widget,
       event->button == 1 &&
       event->type == GDK_2BUTTON_PRESS)
     {
+      meta_core_end_grab_op (gdk_display, event->time);
       return meta_frame_double_click_event (frame, event);
     }