Backtrace:
[ 452.790] 0: /usr/bin/X (xorg_backtrace+0x26) [0x7f2d82f0f2f6]
[ 452.791] 1: /usr/bin/X (0x7f2d82d87000+0x620de) [0x7f2d82de90de]
[ 452.791] 2: /usr/bin/X (0x7f2d82d87000+0x62d4d) [0x7f2d82de9d4d]
[ 452.791] 3: /usr/bin/X (GetPointerEvents+0x303) [0x7f2d82deb2d3]
[ 452.791] 4: /usr/bin/X (0x7f2d82d87000+0x172b56) [0x7f2d82ef9b56]
[ 452.791] 5: /usr/bin/X (miPointerWarpCursor+0xe7) [0x7f2d82ef9fd7]
[ 452.791] 6: /usr/bin/X (0x7f2d82d87000+0x86f61) [0x7f2d82e0df61]
[ 452.791] 7: /usr/bin/X (0x7f2d82d87000+0x17352c) [0x7f2d82efa52c]
[ 452.791] 8: /usr/bin/X (0x7f2d82d87000+0x111fe3) [0x7f2d82e98fe3]
[ 452.791] 9: /usr/bin/X (0x7f2d82d87000+0xfcece) [0x7f2d82e83ece]
[ 452.791] 10: /usr/bin/X (RRPointerScreenConfigured+0x75) [0x7f2d82e840f5]
[ 452.791] 11: /usr/bin/X (RRTellChanged+0x11b) [0x7f2d82e7d89b]
[ 452.791] 12: /usr/bin/X (RRCrtcSet+0x353) [0x7f2d82e7e9d3]
[ 452.791] 13: /usr/bin/X (ProcRRSetCrtcConfig+0x3f3) [0x7f2d82e7f973]
[ 452.791] 14: /usr/bin/X (0x7f2d82d87000+0x4e761) [0x7f2d82dd5761]
[ 452.791] 15: /usr/bin/X (0x7f2d82d87000+0x3d68a) [0x7f2d82dc468a]
[ 452.791] 16: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xed) [0x7f2d80f4276d]
[ 452.791] 17: /usr/bin/X (0x7f2d82d87000+0x3d97d) [0x7f2d82dc497d]
[ 452.791] BUG: triggered 'if (!dev->valuator || dev->valuator->numAxes < 2)'
BUG: ../../dix/getevents.c:849 in scale_to_desktop()
[ 452.791]
Downloaded Precise Beta2, prepared an USB drive to boot from, booted.
Went to Displays.
Unchecked "Mirror displays".
BLAM! Both screens blank, system unresponsive (Ctrl-Alt-Backspace does not work, Ctrl-Alt-F1 does not work, only Magic SysRq does).
I was able to log into the system using ssh from another computer.
The system is a Thinkpad T500 laptop with a second monitor.
System is still unresponsive and produces the same symptoms after upgrading using ppa:xorg-