This problem was originally reported in issue 1578 where one user was trying to test the fix for 1578 but was experiencing a page load that never seems to finish. That is, the JQM load message just sits there spinning.
The page that was being loaded was a markup fragment that contained a data-role="page" div with a form that had @data-ajax="false". If I removed the @data-ajax attribute things seemed to load just fine.
I should've noted in the original report above that the hang can be seen in a phonegap app loaded in the iOS iPhone 4.2 Emulator on the Mac.
This does NOT seem to be a problem with phonegap on Android.
Ok, found the problem ... it is real. :-)
In the $.ajax() callback, we look for elements with @href, @src, and @data-ajax="false" elements, the code then assumes that matching elements will have either @href or @src, which of course forms don't ... they have @action ... so the code throws an exception because thisUrl is undefined.
Patch on its way.
Fix landed on the HEAD:
Confirm fixed in 4.3 iphone simulator on osx.