After some fiddling around and looking at the linux driver, I got
our ethernet card (a PCI card based on an AMD Am79C970 chip) to work.
The important change was to reset the bcnt field.

Configuration file entry I use:

le0 at isa? port 0xd000 irq 10

Changes to netbsd-current driver:

*** if_le.c-	Mon Nov 21 22:59:36 1994
--- if_le.c	Fri Dec  9 17:56:13 1994
***************
*** 399,405 ****
  	ifp->if_flags =
  	    IFF_BROADCAST | IFF_SIMPLEX | IFF_NOTRAILERS | IFF_MULTICAST;
  
! 	if (sc->sc_card != DEPCA)
  		isa_dmacascade(ia->ia_drq);
  
  	/* Attach the interface. */
--- 399,405 ----
  	ifp->if_flags =
  	    IFF_BROADCAST | IFF_SIMPLEX | IFF_NOTRAILERS | IFF_MULTICAST;
  
! 	if (ia->ia_drq != DRQUNK && sc->sc_card != DEPCA)
  		isa_dmacascade(ia->ia_drq);
  
  	/* Attach the interface. */
***************
*** 872,877 ****
--- 872,878 ----
  			sc->sc_arpcom.ac_if.if_ipackets++;
  		}
  			
+ 		cdm->bcnt = -BUFSIZE;
  		cdm->mcnt = 0;
  		cdm->flags |= LE_OWN;
  		NEXTRDS;