detecting isa eth in dual bus m’b

I have caldera openlinux 2.2 kernel 2.2.5 running on a gigabyte pci/isa m’board. pci detection and allocation in bios is set to auto.
some weeks ago I noticed that using a isa ethernet board (realtek), if I unloaded the 8390 module in the kernel module window, I am unable to reload it. Thus, what was once a good isa ethernet install now becomes useless. PCI ethernet boards have no problem as a novell-2000 compatible pci driver module is used.
Is this a result of incompatibilities in the PCI – ISA bridge ?