If I upgrade a package which restarts sshd in its post script, sshd will inherit the file descriptor pointing to this rpm. Unfortunately it does not close it. In particular, if the rpm was on an nfs directory it is no longer possible to unmount this directory unless you physically walk to the machine (this is why I consider it "high" priority) There are similar problems with lpd and maybe other services.
As Jeff (jbj) pointed out: If the rpm is on a CD, it is not possible to unmount the CD!
Hmm.. Isn't this an rpm issue?
I also think that this is an rpm issue. rpm should close the file descriptor before giving control to sshd.
This issue is spread among lots of guilty apps, which in an ideal world would all be closing extra descriptors. A workaround which catches most of these cases is in initscripts-5.69.