quotas

[James Devine]

We have a mail server running postfix/dovecot on ubuntu 9.10 using
ext3 as the underlying filesystem and filesystem quotas turned on.  We
have run into a couple instances of people complaining about being
overquota when they are not and du -s does not seem to match what
quota -v is saying.  This last instance quota -v was about 49500 and
du -s on the user's home directory was about 40000, they had about 700
files total so I can't see inode count causing a problem.  I searched
the rest of the filesystem just to make sure that user did not own any
other files and they did not.  A quotacheck on the filesystem repaired
the issue, quota -v was then showing the same as du -s.  Any ideas why
this might be the case and what I might do to fix this?