PHP Notice when saving custom field group that applies to multiple items

To reproduce:
Create a new custom field group and apply it to multiple items. For example apply it to events by choosing event names or choose grants and apply it to several grant types.
Select several event names. Give the group a name and save.

Notice: Array to string conversion in HTML_QuickForm_Rule_Required->validate() (line 63 of /var/www/myhost/sites/all/modules/civicrm/packages/HTML/QuickForm/Rule/Required.php).

Note: This may only be an error in PHP 5.4+.