In this, now well know, post on fedora-devel (http://lists.fedoraproject.org/pipermail/devel/2011-March/150031.html) Lennart Poettering, systemd author, report :
"So, this is what is implemented for F15 now. For F16 we will make a
minor change on top of this: /var/run and /var/lock will become symlinks
to /run (resp /run/lock), so that we don't have to use bind mounts
anymore which are not the most beautiful thing to use by default, and
confusing to the admin. Due to the implications of symlinks and RPM we
didn't want to make that change in F15.
So the alleged lack for rpm for being capable to change a directory with a symbolic link becomes a blocker to bring forward certain features in FC15. Just for info, being relevant to the bug discussed here.