> > b) it's VIA chipset
>
> I would have to go with "b". ;-)
>
> I see something similar when I test with two disks on the master of
> IDE cable-1 and IDE cable-2.
>
> I wonder if folks that don't have VIA chips see a similar

not sure about newer VIA chips, but older (these for Pentium-I) just
emulated two channel having physically only one. i observed same effect.