For what it's worth I solved this issue by hard coding the page's choice of selection list vs field for state:
PHP Code:
<?php
// fix state validation problem by hard coding the select menu as only option
if (ACCOUNT_STATE == 'true') {
?>
<label class="inputLabel" for="stateZone"><?php echo ENTRY_STATE; ?></label>
<?php
echo zen_draw_pull_down_menu('zone_id', zen_prepare_country_zones_pull_down($selected_country), $zone_id, 'id="stateZone"') . '<span class="alert">' . ENTRY_STATE_TEXT . '</span>';
?>
<br class="clearBoth" />
<?php
}
?>
...otherwise, if I tried to do this through the admin, I got both a select list and a field, which I deemed to be too confusing as an interface. So far it seems to work great.