twitter/bootstrap — pull request #7485 by garvincasimir (2013-04-05 19:10:33+00:00)
Title: Added min-height to .modal-header

You may not always want to add a title for your modal. This change will ensure your close button will not look off if you have no text in the header.

See: http://jsbin.com/ayoqad/1/edit for the effect of change