(BETA5-i386) de0: abnormal interrupt: transmit underflow

I get some strange behaviour with my de0 card ... last stable
behaviour was with 5.2.1-Release, I updated to BETA5 this week.

As long as I do innocet stuff like ping everything seems to work.
Once I transfer any useful data (i.e. make update, ssh, ftp, http,
...) The system responds (after approx 1 and 2 seconds) with
   de0: abnormal interrupt: transmit underflow (raising TX threshold to 96|256)
   de0: abnormal interrupt: transmit underflow (raising TX threshold to 128|512)
and network transfer speed gets so slow I cannot even measure it.
(Ping to my gateway on the local network takes 10 seconds and up.)

By ifconfig de0 down|up I can reset the card and repeat as often
as I please.

The speed problem can be undone by setting debug.mpsafenet=0.

Please tell me if I can give any diagnostics that might help.  Or
if I can test any patches You might work on.

Kind Regards, Robert S.
--
FreeBSD robert3.mpe-garching.mpg.de 5.3-BETA5 FreeBSD 5.3-BETA5 #0:
Tue Sep 21 11:08:16 CEST 2004
root_at_robert3.mpe-garching.mpg.de:/usr/obj/usr/src/sys/ROBERT3  i386