xl problems with 100mbit connections

[Nick Nauwelaerts <nick_(_at_)_wanadoo_(_dot_)_be>]

OK, I've been seeing this for over a year now. I have a OpenBSD 2.9 box
which is connected to a Cisco something switch (forgot the exact model)
and has a 3com 905B card in it:

openbsd2.9 [i386] stable:
xl0 at pci0 dev 14 function 0 "3Com 3c905B 100Base-TX" rev 0x30: irq 10
xl0: command never completed!
exphy0 at xl0 phy 24: 3Com internal media interface

Now, whenever I set this interface to 100mbit (full or half duplex) or
autoselect I start having over 80% packet loss and the connection thus
becomes next to useless. When I force it to 10mbit it doesn't complain
and works like a charm. So I just left the box there on 10mbit, thinking
that is was most likely a cisco problem.

Now I just recently bought about 10 additional 3com 905b cards, to
replace my realtek ones at home. 

openbsd3.1-current [i386] (Fri May 3):
xl0 at pci0 dev 14 function 0 "3Com 3c905B 100Base-TX" rev 0x24: irq 10
xl0: command never completed!
exphy0 at xl0 phy 24: 3Com internal media interface
xl1 at pci0 dev 15 function 0 "3Com 3c905B 100Base-TX" rev 0x30: irq 11
xl1: command never completed!
exphy1 at xl1 phy 24: 3Com internal media interface

When I reboot that particular machine, it comes back up without any
problems. However for some reason my switch (some el cheapo Kirk Style
switch) begins flashing like mad, and says my xl0 is connected as
10mbit. ifconfig xl0 says "no carrier" on the BSD box. When I powercycle
my switch everything goes back to normal (100mbit full-duplex).
The other one, xl1, is connected with a crossed UTP cable to my
neighbour's FreeBSD box. After a reboot the connection went dead, and
ifconfig xl1 said "no carrier" again. Unplugging the UTP cable and
re-plugging it solved this problem again. Also note, both sides of this
connection are forced 100mbit full-duplex as well.

2 other OpenBSD boxes in my internal network, also with 3com 905B cards
have the exact same problem, while other network cards work just fine,
and one Windows box (which dual boots openbsd where it does have the
problem) with a 905B card doesn't have this problem either.

I've verified everything I could think of:
- tested with other OS, no problem
- tested different kernels (generic as well), always the same problem
- tried different network cables (the ones I use are Lucent cables)
- haven't been able to change the switch due to lack of hardware, put
  the problem persists on different sites (at home and at work with a
  cisco switch) as well as with crossover cable.

Has anyone else run into this problem?
Complete dmesg's can be provided.

// nick