odd problem: simple xml building mod breaks game menus

[damocles88]

Look at this tiny little mod:

<GameData>
    <Civilization_BuildingClassOverrides>
        <Row>
            <CivilizationType>CIVILIZATION_AMERICA</CivilizationType>
            <BuildingClassType>BUILDINGCLASS_STONEHENGE</BuildingClassType>
            <BuildingType/>
        </Row>
    </Civilization_BuildingClassOverrides>
</GameData>

This should have removed stone henge from the buildings America can build. Instead, it made the game go crazy. When I load this mod and go to set up a game, all other civs are missing from the choose a civ screen, except for America. When I select America, all the menus disappear completely and I'm left staring at the picture of atlas. I have to alt-f4 out of the game.

How on earth does this little change break the game so badly? I'm using the same xml technique they used to stop barbarians and minor civs building wonders.

Any ideas anyone?