1. Minimize all visible windows.
2. Press the Run program... magic key combination;
Results:
1. dialog appears
2. metacity crashes (not always, most of the time)

Here's some gdb backtrace info:

(gdb) f

+ Trace 62051

    window=0x8135db0, fgeom=0x8135e5c, x=0xbfe0d188, y=0xbfe0d18c)
    at place.c:373
373       meta_topic (META_DEBUG_PLACEMENT,
(gdb) l
368                       "to the focus window; had to move it to avoid the "
369                       "focus window\n",
370                       window->desc);
371         }
372
373       meta_topic (META_DEBUG_PLACEMENT,
374                   "Status:\n"
375                   "  denied focus: %d\n"
376                   "  modal:        %d\n"
377                   "  same app:     %d\n"
(gdb) l
378                   "  overlaps      %d\n",
379                   window->denied_focus_and_not_transient,
380                   window->wm_state_modal,
381                   meta_window_same_application (window, focus_window),
382                   meta_rectangle_intersect (&window->rect,
383                                             &focus_window->rect,
384                                             &overlap)
385                   );
386     }
387
(gdb) p focus_window
$7 = (MetaWindow *) 0x0