Found a nice crasher for xfwm4...

Run xine-ui (CVS HEAD will do) and open various of its windows:: controls,
open file, open playlist, open location, playlist load, playlist editor.
Toggle to and from full-screen mode repeatedly; sooner or later, it'll
segfault. A typical backtrace is attached.  

As far as I can tell, this is happening as a result of a ShapeNotify event
on a window: the CWindow struct looks valid, but it contains a pointer to a
broken Client struct. (It may be that the pointer itself is invalid.)   
  
The window size _suggests_ that the problem window may be xine's full-screen 
window (the size parameters for resize_win() match the screen size).
Certainly, other strange things are happening to xine windows, such as its  
top-level menu gaining a frame...


#0  0x00002b8c64a9cde0 in raise () from /lib/libc.so.6
#1  0x00002b8c64a9e290 in abort () from /lib/libc.so.6
#2  0x00002b8c6410e47b in g_logv () from /usr/lib/libglib-2.0.so.0
#3  0x00002b8c6410e503 in g_log () from /usr/lib/libglib-2.0.so.0
#4  0x0000000000435eff in handleSignal (sig=11) at main.c:128
#5  <signal handler called>
#6  0x000000000042c8fd in frameTop (c=0x6dcd60) at frame.c:115
#7  0x000000000042cba8 in frameY (c=0x6dcd60) at frame.c:159
#8  0x000000000041a582 in client_size (cw=0x6d5250) at compositor.c:648
#9  0x000000000041ceab in fix_region (cw=0x6db5d0, region=12603706)
    at compositor.c:1511
#10 0x000000000041e78c in resize_win (cw=0x6db5d0, x=0, y=0, width=1280,
    height=1024, bw=0, shape_notify=1) at compositor.c:2042
#11 0x000000000041f662 in compositorHandleShapeNotify (display_info=0x5b9170,
    ev=0x7fff48654ba0) at compositor.c:2360
#12 0x000000000041fb1f in compositorHandleEvent (display_info=0x5b9170,
    ev=0x7fff48654ba0) at compositor.c:2498
#13 0x00000000004298bc in handleEvent (display_info=0x5b9170,
    ev=0x7fff48654ba0) at events.c:2163
#14 0x0000000000429b06 in xfwm4_event_filter (xevent=0x7fff48654ba0,
    data=0x5b9170) at events.c:2248
#15 0x00000000004233d3 in eventXfwmFilter (gdk_xevent=0x7fff48654ba0,
    event=0x6d25e0, data=0x6c8150) at event_filter.c:159
#16 0x00002b8c62f71d85 in gdk_events_pending ()
   from /usr/lib/libgdk-x11-2.0.so.0
#17 0x00002b8c62f7257f in gdk_x11_register_standard_event_type ()
   from /usr/lib/libgdk-x11-2.0.so.0
#18 0x00002b8c62f74128 in _gdk_events_queue ()
   from /usr/lib/libgdk-x11-2.0.so.0
#19 0x00002b8c62f7427e in _gdk_events_queue ()
   from /usr/lib/libgdk-x11-2.0.so.0
#20 0x00002b8c64106149 in g_main_context_dispatch ()
   from /usr/lib/libglib-2.0.so.0
#21 0x00002b8c641092b5 in g_main_context_check ()
   from /usr/lib/libglib-2.0.so.0
#22 0x00002b8c641095b6 in g_main_loop_run () from /usr/lib/libglib-2.0.so.0
#23 0x00002b8c62b18252 in gtk_main () from /usr/lib/libgtk-x11-2.0.so.0   
#24 0x0000000000436e1e in main (argc=1, argv=0x7fff48654fb8) at main.c:587


Patches applied: my switch-no-raise patch, and a reversion of the part of rev. 22470 which applies to src/keyboard.c.