unusal fetchmail error

[Kozman Balint <qzy@mp.inf.elte.hu>]

Hi to everyone,

I'm running a local mailserver behind a Sonic pro firewall. Outgoing
messages are sent via exim to the smarthost outside with address revision.
I use fetchmail to get messages from the mailserver outside via pop3.
The problem is with fetchmail: sometimes when it gets defunct after
downloading messages, it becomes a Zombie, and some minutes later when the
new instance of fetchmail comes up, it stops working 'cos "another
fetchmail is running in background" and this way users don't get their
mails.
Is this a kernel problem, or a bug of fetchmail, or what?
(fetchmail gets started via cron)

Thanks in advance, regards:

Balint