@scottjehl told me about this one:
If you load a JQM application, then navigate to another page, you see a slide transition. If you hit the browser back button, you see a reverse slide transition to the initial application page. If you then hit the browser's forward button, you are taken to the page you previously visited instantly with no transition.
Looking into it, the logic for calculating the transition to use in this situation is pretty much the same as it was prior to the navigation code refactor I did. The one difference is that the initial page used to have a boolean false value as its value for the transition property of its urlHistory stack entry. Now it has "none" so the old logic allows the "none" to be used as the transition for the new page.
Landed fix for this on HEAD: