Not that it really matter to make things work... but I injected some fields in the user edit form:
$form['block']['field'] = Array( '#title' => t('Page'), '#type' => 'textfield', '#maxlength' => 10, '#size' => 11, '#default_value' => $edit['field'], );
I cleared them in the update/insert hook_user
$edit['field']=NULL;
but I still get b:0; in the data field of the DB.