[fetchmail]fetchmail problem mails getting replicated

I am using fetchmail with qmail 1.03 as MTA.
fetchmail is run from rc.local ind daemon mode when machine boots up.
The rc.local entry is
/usr/bin/fetchmail -vvaf /root/.fetchmailrc -d 120 --syslog

But I am facing a strange problem.Sometimes the mails get replicated and
when i see the log,it says something like:
1. ***fetchmail: message 1 was not the expected length (398 actual != 387
expected)

This is happening for only certain accounts only.

Please help