Created Issue: Unable to use slipstreaming with SP2013 with April 2013 CU. [19672]

That is not an issue with AutoSPInstaller. It is an issue with SharePoint 2013 April CU requiring March 2013 Public Update to be applied first.

http://sharepoint.nauplius.net/2013/04/slipstreaming-the-sharepoint-2013-april-2013-cumulative-update/

So. Heads-up, or let me know if you have smart workarounds.