Hi, I can confirm this, reading the code of the jform_associations plugin you can see from line 79 to line 111
	
		// Create Form
	
	
		$addform = new SimpleXMLElement( '<form />' );
	
	
		$fields = $addform->addChild( 'fields' );
	
	
		$fields->addAttribute( 'name', $name );
	
	
		$fieldset = $fields->addChild( 'fieldset' );
	
	
		$fieldset->addAttribute( 'name', 'item_associations' );
	
	
		$fieldset->addAttribute( 'description', 'COM_CONTENT_ITEM_ASSOCIATIONS_FIELDSET_DESC' );
	
	
		$fieldset->addAttribute( 'addfieldpath', '/administrator/components/
		com_content/models/fields' );
	
	
		$hasForm = false;
	
	
		foreach ( $languages as $tag=>$language ) {
	
	
		if ( empty( $config['language'] ) || $tag != $config['language'] ) {
	
	
		$hasForm = true;
	
	
		$f = $fieldset->addChild( 'field' );
	
	
		$f->addAttribute( 'name', $tag );
	
	
		$f->addAttribute( 'type', '
		modal_article' );
	
	
		$f->addAttribute( 'language', $tag );
	
	
		$f->addAttribute( 'label', $language->title );
	
	
		$f->addAttribute( 'translate_label', 'false' );
	
	
		}
	
	
		}
	
	
		$form = JForm::getInstance( $id, $addform->asXML() );
	
	
		if ( $hasForm ) {
	
	
		$form->load( $addform, false );
	
	
		$associations = JLanguageAssociations::getAssociations( '
		com_content', '#__content', 'com_content.item', $config['pk'] );
	
	
		if ( count( $associations ) ) {
	
	
		foreach ( $associations as $tag=>$association ) {
	
	
		$form->setValue( $tag, $name, $association->id );
	
	
		}
	
	
		}
	
	
		if ( $config['translate_id'] && isset( $config['translate'] ) ) {
	
	
		$form->setValue( $config['translate'], $name, $config['translate_id'] );
	
	
		}
	
	
		}
		
	
 
As you can see here, right now it is hardcoded to associate just things of the "content" table... Also if you look at the code of the cck_storage_location joomla_category plugin, you will see around the line 323 this: 
	I think this is something that will be developed in the near future but for now is not supported unless you develop your own cck_storage_location and your cck_field plugins...