Description of problem:
Xserver crash occurs on attempt to quit screensaver Flurry. Sometimes it happen even on preview window when I select different screensaver. My DE is KDE 4.5.4 with kwin as window manager.
Crash is not 100% reproductible but for me it happen twice every three attempts. Other GL screensavers like Euphoria or Flux are working fine.

Here's the backtrace:
=======================================
[  5217.986] 0: /usr/bin/X (xorg_backtrace+0x3c) [0x80e7f2c]
[  5217.986] 1: /usr/bin/X (0x8047000+0x5ed56) [0x80a5d56]
[  5217.987] 2: (vdso) (__kernel_rt_sigreturn+0x0) [0x47740c]
[  5217.987] 3: /usr/lib/xorg/modules/libexa.so (exaGetPixmapDriverPrivate+0x35) [0x368945]
[  5217.987] 4: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x51e000+0xc0c3d) [0x5dec3d]
[  5217.987] 5: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x51e000+0xc1298) [0x5df298]
[  5217.987] 6: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x51e000+0xc49d3) [0x5e29d3]
[  5217.987] 7: /usr/lib/libdrm.so.2 (drmHandleEvent+0xf5) [0x88fb45]
[  5217.987] 8: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x51e000+0xc498f) [0x5e298f]
[  5217.987] 9: /usr/bin/X (WakeupHandler+0x52) [0x8073a72]
[  5217.988] 10: /usr/bin/X (WaitForSomething+0x1a2) [0x809f132]
[  5217.988] 11: /usr/bin/X (0x8047000+0x2828e) [0x806f28e]
[  5217.988] 12: /usr/bin/X (0x8047000+0x1b355) [0x8062355]
[  5217.988] 13: /lib/libc.so.6 (__libc_start_main+0xe6) [0x8d3e16]                                                                                                         
[  5217.989] 14: /usr/bin/X (0x8047000+0x1af31) [0x8061f31]                                                                                                                 
[  5217.989] Segmentation fault at address 0x4d                                                                                                                             
[  5217.989]                                                                                                                                                                
Fatal server error:                                                                                                                                                         
[  5217.989] Caught signal 11 (Segmentation fault). Server aborting                                                                                                         
[  5217.989]                                                                                                                                                                
[  5217.989]                                                                                                                                                                
Please consult the Fedora Project support                                                                                                                                   
         at http://wiki.x.org                                                                                                                                               
 for help.                                                                                                                                                                  
[  5217.989] Please also check the log file at "/var/log/Xorg.0.log" for additional information.
=======================================
Version-Release number of selected component (if applicable):
xscreensaver-*-5.12-8.fc14.i686
xorg-x11-server-Xorg-1.9.3-3.fc14.i686
mesa-dri-drivers-7.9-5.fc14.i686
kernel-PAE-2.6.35.10-74.fc14.i686
kdebase-4.5.4-1.fc14.i686

Hardweare:
Dell Lattitude D610
CPU: Pentium M 
GFX: Radeon X300 (RV370)

How reproducible:
66%

Steps to Reproduce:
1. Select Flurry screensaver
2. Click "Test" buton to start screensaver
3. Hit any key or move mouse to stop screensaver
  
Actual results:
twice every three attempts X crash occurs, I'm getting thrown back to login screen

Expected results:
Screensaver exits clean, I'm back to desktop. No crash occurs

Additional info:
Usually I run kwin with composite on, but it doesn't matter, I can reproduce crash with effects off too.

I have some basic tweaks in/etc/Xorg/xorg-conf.d/00-radeon.conf:

Section "Device"
        Identifier  "Videocard0"
        Driver      "radeon"
        Option      "RenderAccel" "true"
        Option      "AccelMethod" "EXA"
        Option      "AccelDFS" "true"
        Option      "DRI" "on"
        Option      "ColorTiling" "true"
        Option      "EnablePageFlip" "on"
        Option      "Monitor-LVDS" "IntDisplay"
        Option      "Monitor-VGA" "ExtVGA"
EndSection