[Exim] Serious bug in 3.040?

I experience a serious bug with Exim 3.040 on my system that corrupts long
emails by omitting characters every now and then. This only happens for
mails longer than a few hundred kb. I can reproduce the problem and it
are always the same characters that are missing in the delivered mail.
I use Exim as smart host, so it is not a bug in file-related transports.

Any ideas?

Michael