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So, I went into /usr/share/xfce4/backdrops (Xubuntu 13.04 raring) and removed all of the links, created when I installed extra gtk2 / gtk3 themes.
Here is what my /usr/share/xfce4/backdrops looked like before I removed all of the links (for example, the bluebird-2010-08-xubuntu.svg link)
drwxr-xr-x 2 root root 4096 Jun 23 18:39 .
drwxr-xr-x 11 root root 4096 Jun 24 20:02 ..
lrwxrwxrwx 1 root root 38 Apr 15 18:05 albatross-2009-10.png -> ../../wallpapers/albatross-2009-10.png
lrwxrwxrwx 1 root root 42 Apr 15 18:05 albatross-wall-source.svg -> ../../wallpapers/albatross-wall-source.svg
-rw-r--r-- 1 root root 457165 May 2 2011 alone.jpg
-rw-r--r-- 1 root root 8847 May 2 2011 Aquarius.svg
lrwxrwxrwx 1 root root 55 Apr 15 18:05 bluebird-2010-08-1920x1200-xubuntu.png -> ../../wallpapers/bluebird-2010-08-1920x1200-xubuntu.png
lrwxrwxrwx 1 root root 54 Apr 15 18:05 bluebird-2010-08-1920x1440-notext.png -> ../../wallpapers/bluebird-2010-08-1920x1440-notext.png
lrwxrwxrwx 1 root root 55 Apr 15 18:05 bluebird-2010-08-1920x1440-xubuntu.png -> ../../wallpapers/bluebird-2010-08-1920x1440-xubuntu.png
lrwxrwxrwx 1 root root 45 Apr 15 18:05 bluebird-2010-08-xubuntu.svg -> ../../wallpapers/bluebird-2010-08-xubuntu.svg
-rw-r--r-- 1 root root 484135 May 2 2011 Butterfly.jpg
-rw-r--r-- 1 root root 201906 May 2 2011 CleanBlue.jpg
-rw-r--r-- 1 root root 446538 May 2 2011 Crow.jpg
-rw-r--r-- 1 root root 746954 May 2 2011 cumberlandfalls2.jpg
-rw-r--r-- 1 root root 557843 May 2 2011 dog-rose.jpg
-rw-r--r-- 1 root root 501257 May 2 2011 firework.jpg
-rw-r--r-- 1 root root 761374 May 2 2011 Forrest.jpg
lrwxrwxrwx 1 root root 44 Apr 15 18:05 greybird-wall-1920x1200.png -> ../../wallpapers/greybird-wall-1920x1200.png
lrwxrwxrwx 1 root root 34 Apr 15 18:05 greybird-wall.svg -> ../../wallpapers/greybird-wall.svg
-rw-r--r-- 1 root root 152397 May 2 2011 hippeastrum.jpg
-rw-r--r-- 1 root root 257314 May 2 2011 kanttarelli.jpg
-rw-r--r-- 1 root root 127838 May 2 2011 Klivia.jpg
-rw-r--r-- 1 root root 142038 May 2 2011 mgla_wiosenna.jpg
-rw-r--r-- 1 root root 57252 May 2 2011 moon_venus.jpg
-rw-r--r-- 1 root root 275569 May 2 2011 ohio-sky.jpg
-rw-r--r-- 1 root root 285698 May 2 2011 ondasblue.jpg
-rw-r--r-- 1 root root 298554 May 2 2011 opole-sky.jpg
-rw-r--r-- 1 root root 90721 May 2 2011 paltanen.jpg
-rw-r--r-- 1 root root 228257 May 2 2011 park.jpg
-rw-r--r-- 1 root root 632001 May 2 2011 primulag.jpg
-rw-r--r-- 1 root root 576099 May 2 2011 Squirrel.jpg
-rw-r--r-- 1 root root 61761 May 2 2011 Szarkakoi_fa.jpg
-rw-r--r-- 1 root root 246814 May 2 2011 tipas.jpg
-rw-r--r-- 1 root root 139423 May 2 2011 Valo_1.jpg
-rw-r--r-- 1 root root 294955 May 2 2011 vect_or.jpg
-rw-r--r-- 1 root root 591808 May 2 2011 Violet.jpg
-rw-r--r-- 1 root root 99907 May 2 2011 xfce-evil.jpg
-rw-r--r-- 1 root root 366622 May 2 2011 xfce-gradiented.png
-rw-r--r-- 1 root root 977787 May 2 2011 xfce-transparent.png
lrwxrwxrwx 1 root root 18 Jun 20 18:23 xubuntu-precise-right.png -> xubuntu-raring.png
-rw-r--r-- 1 root root 589196 Apr 14 00:57 xubuntu-quantal.png
-rw-r--r-- 1 root root 418556 Apr 14 00:57 xubuntu-raring.png
I removed all of the links and now "Desktop Settings.." pops right up without consuming all of the CPU. I suspect removing the links to the .svg files would have sufficed rather than removing all of the links.
Xfce 4.12
Manjaro 0.8.12 (x86_64)
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