Module "forget" the start term id previously configured

Hello
if you choose a sub level term as the start of the menu, when you save and then come back to the block configuration; you see that's the start come back to "root" on the configuratio form.
Line 57 variable_set should be variable_get

  	$form['root_term'] = array
  	(
  		'#type' => 'select',
  		'#title' => t('Root term'),
  		'#options' => $options,
  		'#default_value' => variable_get("taxonomy_blocks_vid_{$delta}_root",0),
  	);