I've got /opt/zimbra/store mounted to an NFSv4 store

Code:
zimbra@mail: df -h | grep -i /store
   nas.dchil.loc:/servers/zimbra/store
     788G  197M  748G   1% /opt/zimbra/store
Plenty of space available.

But if I restart zimbra, I get a WARNING about not enough disk space,

WARNING: Disk space below threshold for /opt/zimbra/store.


Code:
zimbra@mail-:~$ zmcontrol restart
Host mail.dchil.loc
        Stopping stats...Done.
        Stopping mta...Done.
        Stopping spell...Done.
        Stopping snmp...Done.
        Stopping cbpolicyd...Done.
        Stopping archiving...Done.
        Stopping antivirus...Done.
        Stopping antispam...Done.
        Stopping imapproxy...Done.
        Stopping memcached...Done.
        Stopping mailbox...Done.
        Stopping logger...Done.
        Stopping zmconfigd...Done.
        Stopping ldap...Done.
Host mail.dchil.loc
        Starting ldap...Done.
        Starting zmconfigd...Done.
        Starting logger...Done.
df: no file systems processed
        WARNING: Disk space below threshold for /opt/zimbra/store.
        Starting mailbox...Done.
        Starting antispam...Done.
        Starting antivirus...Done.
        Starting snmp...Done.
        Starting spell...Done.
        Starting mta...Done.
        Starting stats...Done.
Clearly there's enough space.

Is there some Zimbra config I need to do? Or is this a bug?