Form with managed files weird behaviour on form error - forms

Question

I have created a content type with an associated image field.
Each user is able to see a list of all the nodes of this content type and should be able to upload a new image in the appropriate field.
I've tried many solutions, but in the end I'm trying with a form and managed files.
In the page with the list of all the nodes I'm creating a lightbox with a form for each node.
Each form is created like this:
function coverupload_form($form, &$form_state, $uid, $relid) {
$form['#attributes']['id'] = 'coverup-'.$relid;
$form_state['storage']['rid'] = $relid;
$cliente = cataloghi_user_edit_get_cliente($uid);
$release = node_load($relid);
$form['cover'] = array(
'#title' => 'Carica la cover per la release '.$release->title,
'#description' => 'I file caricati devono avere estensione \'.jpeg\', risoluzione di 1440x1440 e dimensione massima di 5MB',
'#type' => 'managed_file',
'#upload_location' => 'public://clienti/'.$cliente->title.'/cover',
'#upload_validators' => array(
'file_validate_extensions' => array('jpeg, jpg'),
// Pass the maximum file size in bytes
'file_validate_size' => array(5*1024*1024),
'file_validate_image_resolution' =>array('1440x1440', '1440x1440'),
),
);
$form['submit'] = array(
'#type' => 'submit',
'#value' => t('CARICA'),
);
return $form;
}
function coverupload_form_submit($form, &$form_state) {
$file = file_load($form_state['values']['cover']);
// Change status to permanent.
$file->status = FILE_STATUS_PERMANENT;
// Save.
file_save($file);
$nodo = node_load($form_state['storage']['rid']);
$nodo->field_release_copertina['und'][0] = (array)$file;
if($nodo = node_submit($nodo)) { // Prepare node for saving
node_save($nodo);
}
}
All the forms have display: none, and when the user click on the cover upload button only the corresponding form is showed in the lightbox.
Well, everything works fine when the image is validated.
The problems start when the image is not validated (like if it's below 1440x1440px).
If I check the lightbox with the inspector, the correct number of forms is generated but they all refer to the same node (so they all have id 'coverup-17' for example).
I have checked everything, and it seems like I pass the correct values to the form everytime, so I'm starting to think that it may be a problem connected with my poor understanding of forms.
Would it be better to try a different type of approach?
Thanks and sorry for if this is a bit messy...

Answer 1

I managed to solve the problem.
It depended on the fact that I had multiple instances of the same form on the same page.
I implemented hook_forms().
function mymodule_forms($form_id, $args) {
$forms = array();
if(strpos($form_id, 'coverupload_form_') === 0) {
$forms[$form_id] = array(
'callback' => 'coverupload_form',
'callback arguments' => array($args[0], $args[1]),
);
}
return $forms;
}
and then I changed my form call to
drupal_render(drupal_get_form('coverupload_form_'.$relid, $arg1, $arg2));