Hmmmmmmm, sounds fishy. Tell us about the Hereford cow, adn post her ereg number for us.
Much as I hate to agree with ollie, one plausible explanation is that the Hereford cow is part Simmental.
When some of the 1st fullblood simmies were crossed with Herefords, then F2 crosses made, there were solid face cattle in the mix indicating that the white face in Simmental had a different inheritance that the white face in Herefords. So, it was then possible to have solid faced cattle born from white faced animals.
I'd be interested to see the pedigree of that Hereford cow, to see if she traces back to some of the bulls that questions were raised about.
mtnman