BOGUS files generated by procmail???

After switching over to Redhat Linux 6.1, some of the users' procmail
processes started generating files in the mail spool directory of
form

        BOGUS.udername.wxyz

where wxyz is an apparently random character string.  Only one BOGUS
file is generated per user, and only a select number of users have these
files.  Any clues?

Thanks,

Dave Stone