There is a bug in one of the packages involved.
How to fix.
yum erase control-center-extra
when that has finished
yum downgrade control-center control-center-filesystem gnome-desktop
When that finishes, the nautilus windows stop spawning. Even after reboot things are fine.
If you can't get a terminal up while the nautilus issue is going on, reboot into run level 3 by using the grub menu to edit the kernel commands and adding a space then 3 to the end of the line.
Log in as a user, then su - to root, then use the yum commands I listed.
Of course you will lose focus follows mouse, but it's better than the alternative !
For future reference, how to find out what got installed after the fact.
shows you the last things yum did, and they have ID numbers.
Pick the highest ID for the info you need.
yum history info <ID>
shows you what you installed and the dependencies that were also installed/upgraded.
Then you can backtrack. It's best to downgrade them all at once, so that dependencies are met properly.
I uninstalled control-center-extra first because it's difficult to downgrade something that wasn't installed before !
(although that might fix the nautilus bug if you downgraded all the packages at once including control-center-extra)
I've now posted a bug at Redhat bugzilla.