Displaying, hiding, and displaying the same modal multiple times will sometimes fail, leaving the modal backdrop fade in place and no modal displayed.

This has been reproduced in Safari.

Steps to reproduce:

1. Go to this page: http://getbootstrap.com/javascript/#modals
2. Click on the "Launch modal demo" button 10-20 times.
3. You have reproduced this error is the dialog does not appear at least once.