[Exim] Slow local delivery on libc5

Hello,

I have an interesting situation. Exim is fed by fetchmail. Exim is
using the procmail pipe for local delivery. When I am distributing
the mails from the queue with 'exim -q -v', it takes about 1 to 2
seconds to deliver each message on a libc5 system. On glibc
(2.0/2.1), Exim compiled with the same options and using the exact
same config file delivers as fast as it should, 20-40 mails/sec.

I haven't done any benchmarks for the timings, they're only from
manual observation. The problem is not dependent on queue size,
kernel version, distribution or hardware. Exim version 3.02, OS is
Linux, libc5 was on Slackware 3.4 and Debian 1.2, glibc was on RH 5.2
and Mandrake 6.0.

This problem is not killing me, but it will be very interesting to
know why it happens?

Thanks for any hints.