Cory Doctorow writing at Boing Boing describes the Cupertino effect as: the technical term for a correct word that is consistently erroneously replaced by spell-checkers.
Apparently this came from Microsoft Word 97 consistent replacement of co-operation (a correct British spelling) with Cupertino (the home town of Apple Inc.). A less extreme example was when I first started off in PR I used to find that the Word 97 tried to replace liasion with liason (the US spelling) despite the spell checker being in UK English mode.
Kudos: When spellcheckers attack: The Cupertino Effect by Cory Doctorow for Boing Boing (December 14, 2008)