$ gdb /usr/lib/unity-settings-daemon/unity-settings-daemon
...
(unity-settings-daemon:26179): Gdk-ERROR **: The program 'unity-settings-daemon' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 139 error_code 8 request_code 134 (SYNC) minor_code 8)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the GDK_SYNCHRONIZE environment
   variable to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

Thread 1 "unity-settings-" received signal SIGTRAP, Trace/breakpoint trap.
0x00007ffff63d2de1 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
(gdb) bt
#0  0x00007ffff63d2de1 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#1  0x00007ffff63d5521 in g_log_writer_default () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007ffff63d397c in g_log_structured_array () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3  0x00007ffff63d3c79 in g_log_structured () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#4  0x00007ffff57ee66e in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#5  0x00007ffff57fb9b3 in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#6  0x00007ffff4a3ec8d in _XError () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#7  0x00007ffff4a3bbb7 in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#8  0x00007ffff4a3bc75 in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#9  0x00007ffff4a3cb88 in _XReply () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#10 0x00007ffff5375c76 in XSyncListSystemCounters () from /usr/lib/x86_64-linux-gnu/libXext.so.6
#11 0x00007ffff79b4c0e in ?? () from /usr/lib/x86_64-linux-gnu/libunity-settings-daemon.so.1


$ GDK_SYNCHRONIZE=1 gdb /usr/lib/unity-settings-daemon/unity-settings-daemon
...
(unity-settings-daemon:26916): Gdk-ERROR **: The program 'unity-settings-daemon' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 154 error_code 8 request_code 134 (SYNC) minor_code 8)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the GDK_SYNCHRONIZE environment
   variable to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

Thread 1 "unity-settings-" received signal SIGTRAP, Trace/breakpoint trap.
0x00007ffff63d2de1 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
(gdb) bt
#0  0x00007ffff63d2de1 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#1  0x00007ffff63d5521 in g_log_writer_default () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#2  0x00007ffff63d397c in g_log_structured_array () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#3  0x00007ffff63d3c79 in g_log_structured () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#4  0x00007ffff57ee66e in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#5  0x00007ffff57fb9b3 in ?? () from /usr/lib/x86_64-linux-gnu/libgdk-3.so.0
#6  0x00007ffff4a3ec8d in _XError () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#7  0x00007ffff4a3bbb7 in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#8  0x00007ffff4a3bc75 in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#9  0x00007ffff4a3cb88 in _XReply () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#10 0x00007ffff4a3857d in XSync () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#11 0x00007ffff4a3861b in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#12 0x00007ffff4a3f60f in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#13 0x00007ffff5376a33 in XSyncCreateAlarm () from /usr/lib/x86_64-linux-gnu/libXext.so.6