Using comment_driven_save in foreach loop results in all comments > 1 being submitted incorrectly

I am using the following function in a custom module, in a hook_nodeapi:

foreach ($node->field_daily_report_equipment_use as $key => $item) {
$equipnode = node_load($item['nid']);
if(certain conditions) {
$comment = '';
$equipmentnode = '';
$comment['comment'] = 'Usage is now' . $node->field_daily_report_equip_usage[$key]['value'];
$comment['uid'] = $node->uid;
$comment['nid'] = $node->field_daily_report_equipment_use[$key]['nid'];
$equipmentnode['field_equipmentlastusagecount'][0]['value'] = $node->field_daily_report_equip_usage[$key]['value'];
$equipmentnode['field_equipmentlastusagerecorded'][0]['value']['date'] = date('n/j/Y', strtotime($node->field_daily_report_date[0]['value']));
$equipmentnode['field_equipmentlastsrvtime'][0]['value']['date'] = date('n/j/Y', strtotime($equipnode->field_equipmentlastsrvtime[0]['value']));
comment_driven_save($equipmentnode, $comment, $errors);
}
}

For the first run through the foreach (or if there is only one row in the array) the comment_driven_save works perfectly. However, on subsequent runs, the submitted comment is malformed, with the comment "2", submittted by "Anonymous", and comment_driven properties not being applied to the node (in fact, no new node revision is created).

I've dumped the $comment and $equipmentnode variables prior to comment_driven_save on all runs, and the data is good (correct comment, uid, nid, and driven properties).

Any ideas? Is there something obviously wrong in my code (certainly a possibility)?