<!-- Deivison -->
/* Original comentado
if ($e->source_model) {
// determine callback for the source model
$factoryName = (string)$e->source_model;
$method = false;
if (preg_match('/^([^:]+?)::([^:]+?)$/', $factoryName, $matches)) {
array_shift($matches);
list($factoryName, $method) = array_values($matches);
}

$sourceModel = Mage::getSingleton($factoryName);
if ($sourceModel instanceof Varien_Object) {
$sourceModel->setPath($path);
}
if ($method) {
if ($fieldType == 'multiselect') {
$optionArray = $sourceModel->$method();
} else {
$optionArray = array();
foreach ($sourceModel->$method() as $value => $label) {
$optionArray[] = array('label' => $label, 'value' => $value);
}
}
} else {
$optionArray = $sourceModel->toOptionArray($fieldType == 'multiselect');

}
$field->setValues($optionArray);
}
*/

/*Colocar esse no lugar*/
if ($e->source_model) {
$sourceModel = Mage::getSingleton((string)$e->source_model);
if ($sourceModel instanceof Varien_Object) {
$sourceModel->setPath($path);
}
if(is_object($sourceModel)){
$field->setValues($sourceModel->toOptionArray($fieldType == 'multiselect'));
} else {
Mage::log($e->source_model);
}
}
<!-- Deivison -->