Update Execute Params do not persist

I have been trying to update numerous records with the one doctrine_query object (which could be my problem) and passing the query execute params to persist to the dbase. eg

$q = Doctrine_Query::create()
->update('TdPackageType pt')
->set('pt.name', '?')
->set('pt.group_type_id', '?')
->where('pt.id = ?')
;

Then iterating over an array of values, passing the required values to the execute method eg
foreach($foobars as $foobar) {
$q->execute(array($foobar[0], $foobar[1], $foobar[2]));
}

I thought this the best way by creating only the one query instance and then assigning the vars as required. Trouble being, the data did not persist? I had no errors returned from Doctrine - eg I had the correct number of matched params - but the update would not update. To move on I ended up instantiating a new query object each time I iterated over my array of data values. eg

foreach($foobars as $foobar) {

$q = Doctrine_Query::create()
->update('TdPackageType pt')
->set('pt.name', '?', $foo[0])
->set('pt.group_type_id', '?', $foo[1])
->where('pt.id = ?', $foo[2])
;

$q->execute();
}

The values did then persist correctly to the dbase? Am I missing something really fundamental here? eg I would have thought the first code struct was a much better design to re-use the one query object. Or is it as silly as me not adding a hydration method to the execute method?

Any all help appreciated.
Thanks
Kyle