Date Format and CiviContribute/Data Form Confirmation Page
The bug come from QuickForm being used to render in "freeze" mode (read-only) for the contribution confirm page.

The bug had been reported here:
https://issues.civicrm.org/jira/browse/CRM-14588

I wrote a patch for it against CiviCRM 4.7 (master dev branch), but it should be easy to apply on 4.6:
https://github.com/civicrm/civicrm-core/pull/5729

Could you test the patch to see if it fixes the issue? If you are not familiar with patches, you can download the file from the pull-request:
https://github.com/mlutfy/civicrm-core/blob/47-crm14588/CRM/Core/Form/Renderer.php

Then click on the "raw" link, which leads to:
https://raw.githubusercontent.com/mlutfy/civicrm-core/47-crm14588/CRM/Core/Form/Renderer.php

You can then save this file and replace the file in your local CiviCRM installation.