In the 2.5.5 T3 framework update, the base-bs3\html\layouts\joomla\content\info_block\publish_date.php file contains invalid information for the parameter that is specified.
On line 17, the itemprop equals "dateModified", however the content is specified as $displayData['item']->publish_up instead of $displayData['item']->modified.
Shouldn't it be the latter?