Comment 7 for bug 831336

@Thomas, it does sound like a compiz bug, however "CompositorRunning: None" indicates no compiz. (I thought that would detect gnome-shell/mutter too but perhaps not). In any case, GdmLog2.txt shows:

*** glibc detected *** /usr/bin/Xorg: free(): corrupted unsorted chunks: 0x0000000002b844c0 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x78a96)[0x7f2b9762ba96]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x6c)[0x7f2b9762fd7c]
/usr/bin/Xorg(DeletePassiveGrab+0x40)[0x445df0]
/usr/bin/Xorg(FreeResource+0x124)[0x44e2c4]
/usr/bin/Xorg(DeletePassiveGrabFromList+0x182)[0x4461a2]
/usr/bin/Xorg(AddPassiveGrabToList+0x22d)[0x44675d]
/usr/bin/Xorg(ProcGrabButton+0x212)[0x43b8d2]
/usr/bin/Xorg[0x42fb39]
/usr/bin/Xorg[0x4232ae]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7f2b975d430d]
/usr/bin/Xorg[0x42359d]

Which is why I asked about lightdm vs. gdm. That log shows a 8/12 build date on xserver, which seems to correspond with the timeframe of 2 weeks. So, while xterm might be triggering it, it's looking more like an xserver bug to me.