look at https://bugzilla.redhat.com/show_bug.cgi?id=887763#c13 util-linux-2.22.2-3.fc18.x86_64 kills output of "mount" completly which leads to break also "df" and who knows what else
or if you would not braindead mangle around with /etc/mtab in the SPEC-file there would no need for reboot or manually re-create the symlink after a yum update - jesus christ this is a SYMLINK and why in the world would a symlink to /proc/mount have to be touched from anything but the kernel or systemd? https://bugzilla.redhat.com/show_bug.cgi?id=887763#c20
Well, there is %post rm -f /etc/mtab ln -s /proc/mounts /etc/mtab in the spec file, maybe it should be improved to use %post if [ ! -L /etc/mtab ]; then rm -f /etc/mtab ln -s /proc/mounts /etc/mtab fi but it still does not explain why _you_ have the problem with update and on all others systems it works.
Let's continue at bug #887763. *** This bug has been marked as a duplicate of bug 887763 ***