After pulling in a few recent patches I've been having problems with xmonad crashing when I close windows from Thunderbird. I haven't extensively tested whether there are other applications that this happens with. xmonad dies with the following information. I'm compiling with ghc 6.6 on Linux. Let me know if there is some additional information that I can provide. Xlib: extension "XINERAMA" missing on display ":0.0". test: 24: /home/geoffw/.dmenu_cache: unexpected operator test: 24: /home/geoffw/.dmenu_cache: unexpected operator test: 24: /home/geoffw/.dmenu_cache: unexpected operator *** glibc detected *** /home/geoffw/bin/xmonad: free(): invalid pointer: 0x0818d7a4 *** ======= Backtrace: ========= /lib/tls/i686/cmov/libc.so.6[0xb7d637cd] /lib/tls/i686/cmov/libc.so.6(cfree+0x90)[0xb7d66e30] /usr/lib/libX11.so.6(XFree+0x1d)[0xb7efbdbd] /home/geoffw/bin/xmonad[0x80b0be8] ======= Memory map: ======== 08048000-0818b000 r-xp 00000000 03:03 3604679 /home/geoffw/bin/xmonad 0818b000-0819c000 rwxp 00143000 03:03 3604679 /home/geoffw/bin/xmonad 0819c000-081e0000 rwxp 0819c000 00:00 0 [heap] b7900000-b7921000 rwxp b7900000 00:00 0 b7921000-b7a00000 ---p b7921000 00:00 0 b7b00000-b7c00000 rwxp b7b00000 00:00 0 b7c0d000-b7c18000 r-xp 00000000 03:03 2900764 /lib/libgcc_s.so.1 b7c18000-b7c19000 rwxp 0000a000 03:03 2900764 /lib/libgcc_s.so.1 b7c19000-b7cda000 r-xs 00000000 00:08 311820296 /SYSV00000000 (deleted) b7cda000-b7cdc000 rwxp b7cda000 00:00 0 b7cdc000-b7cef000 r-xp 00000000 03:03 2900078 /lib/tls/i686/cmov/libpthread-2.5.so b7cef000-b7cf1000 rwxp 00013000 03:03 2900078 /lib/tls/i686/cmov/libpthread-2.5.so b7cf1000-b7cf3000 rwxp b7cf1000 00:00 0 b7cf3000-b7cf7000 r-xp 00000000 03:03 2311161 /usr/lib/libXdmcp.so.6.0.0 b7cf7000-b7cf8000 rwxp 00003000 03:03 2311161 /usr/lib/libXdmcp.so.6.0.0 b7cf8000-b7cfa000 r-xp 00000000 03:03 2311140 /usr/lib/libXau.so.6.0.0 b7cfa000-b7cfb000 rwxp 00001000 03:03 2311140 /usr/lib/libXau.so.6.0.0 b7cfb000-b7cfc000 rwxp b7cfb000 00:00 0 b7cfc000-b7e37000 r-xp 00000000 03:03 2900016 /lib/tls/i686/cmov/libc-2.5.so b7e37000-b7e38000 r-xp 0013b000 03:03 2900016 /lib/tls/i686/cmov/libc-2.5.so b7e38000-b7e3a000 rwxp 0013c000 03:03 2900016 /lib/tls/i686/cmov/libc-2.5.so b7e3a000-b7e3d000 rwxp b7e3a000 00:00 0 b7e3d000-b7e44000 r-xp 00000000 03:03 2900080 /lib/tls/i686/cmov/librt-2.5.so b7e44000-b7e46000 rwxp 00006000 03:03 2900080 /lib/tls/i686/cmov/librt-2.5.so b7e46000-b7e8a000 r-xp 00000000 03:03 2310430 /usr/lib/libgmp.so.3.4.1 b7e8a000-b7e8b000 rwxp 00044000 03:03 2310430 /usr/lib/libgmp.so.3.4.1 b7e8b000-b7eb0000 r-xp 00000000 03:03 2900043 /lib/tls/i686/cmov/libm-2.5.so b7eb0000-b7eb2000 rwxp 00024000 03:03 2900043 /lib/tls/i686/cmov/libm-2.5.so b7eb2000-b7ebf000 r-xp 00000000 03:03 2314013 /usr/lib/libXext.so.6.4.0 b7ebf000-b7ec0000 rwxp 0000d000 03:03 2314013 /usr/lib/libXext.so.6.4.0 b7ec0000-b7fad000 r-xp 00000000 03:03 2311650 /usr/lib/libX11.so.6.2.0 b7fad000-b7fb1000 rwxp 000ed000 03:03 2311650 /usr/lib/libX11.so.6.2.0 b7fb1000-b7fb2000 rwxp b7fb1000 00:00 0 b7fb2000-b7fb4000 r-xp 00000000 03:03 2311665 /usr/lib/libXinerama.so.1.0.0 b7fb4000-b7fb5000 rwxp 00001000 03:03 2311665 /usr/lib/libXinerama.so.1.0.0 b7fb5000-b7fb7000 r-xp 00000000 03:03 2900041 /lib/tls/i686/cmov/libdl-2.5.so b7fb7000-b7fb9000 rwxp 00001000 03:03 2900041 /lib/tls/i686/cmov/libdl-2.5.so b7fd0000-b7fd2000 rwxp b7fd0000 00:00 0 b7fd2000-b7feb000 r-xp 00000000 03:03 2900027 /lib/ld-2.5.so b7feb000-b7fed000 rwxp 00019000 03:03 2900027 /lib/ld-2.5.so bfc41000-bfc58000 rwxp bfc41000 00:00 0 [stack] ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] The application 'Gecko' lost its connection to the display :0.0; most likely the X server was shut down or you killed/destroyed the application. The application 'Gecko' lost its connection to the display :0.0; most likely the X server was shut down or you killed/destroyed the application. The application 'Gecko' lost its connection to the display :0.0; most likely the X server was shut down or you killed/destroyed the application. Xlib: extension "XINERAMA" missing on display ":0.0". test: 24: /home/geoffw/.dmenu_cache: unexpected operator