I can't duplicate that problem and I don't think this merge proposal makes many changes to the code. Which version of gnome-screensaver do you have installed? Because your gdb output seems to say something about a missing ubuntu-lock-on-suspend gsettings key? I've never really learned how to use gdb though.

$ XDG_CURRENT_DESKTOP=Unity gdb gnome-control-center
GNU gdb (GDB) 7.5.91.20130417-cvs-ubuntu
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/bin/gnome-control-center...(no debugging symbols found)...done.
(gdb) start
Temporary breakpoint 1 at 0x71c0
Starting program: /usr/bin/gnome-control-center 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Temporary breakpoint 1, 0x000055555555b1c0 in main ()
(gdb) step
Single stepping until exit from function main,
which has no line number information.
[New Thread 0x7fffeedc7700 (LWP 22969)]
[New Thread 0x7fffb30c5700 (LWP 22970)]
[New Thread 0x7fffb28c4700 (LWP 22971)]
[New Thread 0x7fffb1c22700 (LWP 22973)]
[Thread 0x7fffb28c4700 (LWP 22971) exited]
[New Thread 0x7fffb28c4700 (LWP 22998)]
[New Thread 0x7fffb1421700 (LWP 22999)]
[New Thread 0x7fffb0c20700 (LWP 23000)]
[New Thread 0x7fffa3fff700 (LWP 23001)]

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_set: assertion 'self != NULL' failed
[New Thread 0x7fffa37fe700 (LWP 23002)]
[New Thread 0x7fffa2ffd700 (LWP 23003)]
[New Thread 0x7fffa27fc700 (LWP 23004)]
[New Thread 0x7fffa1ffb700 (LWP 23005)]

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_has_key: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_has_key: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_has_key: assertion 'self != NULL' failed

** (gnome-control-center:22938): CRITICAL **: gee_abstract_map_has_key: assertion 'self != NULL' failed
Error setting crash reporting: GDBus.Error:org.freedesktop.DBus.Error.AuthFailed: Not authorized.
Error setting metrics reporting: GDBus.Error:org.freedesktop.DBus.Error.AuthFailed: Not authorized.
Error setting crash reporting: GDBus.Error:org.freedesktop.DBus.Error.AuthFailed: Not authorized.
Error setting metrics reporting: GDBus.Error:org.freedesktop.DBus.Error.AuthFailed: Not authorized.

(gnome-control-center:22938): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
0x00007ffff581eea5 in __libc_start_main () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) quit
A debugging session is active.

	Inferior 1 [process 22938] will be killed.

Quit anyway? (y or n) y