[background] wallpapers in grid are too small, take long time to load

1. From GNOME Shell, right-click on the desktop and select Change Background…
(If not running GNOME Shell, run XDG_CURRENT_DESKTOP=GNOME gnome-control-center background )
2. Click on the big wallpaper button

What should happen
================
The default wallpapers show up within about a second or two. There's room for about 9 wallpapers that fully fill the white part of the window (3 rows and 3 columns although the bottom row only shows the top half of the wallpapers).

What happens
===========
Recently in Saucy, the wallpapers started showing up much smaller than they should. There's room for about 16 in a single row. Also the wallpapers take much, much longer to load than previously. On my laptop, it took about 37 seconds for the first row of wallpapers to finish showing up. Screenshot attached.

Notably this does not affect Ubuntu 13.04 with the GNOME3 PPA which includes quite a bit of GNOME 3.8 backported including GTK+ 3.8.2. The GNOME3 PPA does not currently include an updated gnome-control-center and gnome-settings-daemon (Ubuntu 13.04 ships 1:3.6.3-0ubuntu24.1).

https://launchpad.net/~gnome3-team/+archive/gnome3/+packages?field.series_filter=raring

This has not yet been reported in gnome-control-center's bugzilla nor have any relevant commits been made to the background panel in trunk: https://git.gnome.org/browse/gnome-control-center/log/panels/background

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: gnome-control-center 1:3.6.3-0ubuntu30
ProcVersionSignature: Ubuntu 3.10.0-5.15-generic 3.10.2
Uname: Linux 3.10.0-5-generic x86_64
ApportVersion: 2.11-0ubuntu1
Architecture: amd64
Date: Fri Jul 26 22:48:29 2013
InstallationDate: Installed on 2013-06-14 (42 days ago)
InstallationMedia: Ubuntu-GNOME 13.10 "Saucy Salamander" - Alpha amd64 (20130613)
MarkForUpload: True
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)
usr_lib_gnome-control-center:
 activity-log-manager 0.9.7-0ubuntu4
 deja-dup 27.3.1-0ubuntu1
 gnome-control-center-signon 0.1.7~+13.10.20130724.1-0ubuntu1
 gnome-control-center-unity 1.3daily13.06.14.1-0ubuntu1
 indicator-datetime 12.10.3+13.10.20130725-0ubuntu1