[Dovecot] Corrupted index cache file [...] invalid record size

[Lorens]

I get this error every single time some of my users log in:

Error: POP3(${user}): Corrupted index cache file /${userdir}/dovecot.index.cache: invalid record size

The named file seems to be deleted as soon as corruption is
found.

This only affects some users. I thought the affected users had
in common that they are using POP3 in "leave-messages-on-server"
mode, and that their mailboxes are big ( > 100 MB). However I've
found a few counterexamples, few and far between (not every
login) but still.

Google's no help, for once :-)

Could this be a locking problem, a bug with big Maildirs
(counterexamples being few), or what?  I know some of my users
have had problems logging several IMAP clients into the smae
account at the same time, wouldn't put it past some of those
with problems to be trying the same with POP.

I know that a detected cache corruption is merely that, but I
find the error message annoying :-)

Configuration:

        v1.0-stable (0.99.20050712-2 from debian unstable)
	
        Maildir only
	
        Default locking (nothing mentioned in conf file)

        Access over NFS

        mmap_disable = yes (wiki says to disable mmap to use
        indexes on NFS).

Thanks for any pointers.