When knfsd is restarted after reboots, the old rmtab, etab, and xtab files
in /var/lib/nfs aren't cleared. I'm not actually sure if this is a bug as
far as the NFS protocol goes, but it's annoying.
No, it is not. Those files help the nfs server to realize what was the last
known status for its clients on startup.
Without those every client will be forced to remount the NSF dirs when the NFS
server goes down.