>   Does that mean that the card isn't responding properly to what the driver
> is telling it, but there still might be some hope of figuring out a way to
> make the card stay full duplex when ifconfig requests full duplex?
> 
>   Is there a straightforward way to patch the driver to not change the
> autonegotiated settings (recall that the full-duplex light on the switch
> is on until ifconfig runs)?

I don't think this is possible.  It's the responsibility of the driver 
to tweak certain registers once negotiation has been completed.  I
have an internal version of the tlp driver which mostly autonegotiates
with the Macronix 98715AEC-C parts (such as used in the Sohoware 
fast ethernet card).  However, there are some pathological states which 
it can get into, and the code is not as general as it should be.

I haven't tested full duplex since before some recent bugfixes.
Full duplex was generating too many errors when I last used it,
so I turned it off.  That at least lets it work by default in most
places, since the negotiation is completed correctly.