I noticed some problems on my site when using a Blackberry Curve 8530 with BB 5.0, specifically related to things that use jQM dialogs. I tested on both the RC2 and latest docs/demos sites and the same problem exists there as well. For anything that uses the dialogs functionality, closing a dialog comes back to the wrong page.
For instance, on the Select form element page: http://jquerymobile.com/test/docs/forms/selects/
Using any of the non-native select demos there that result in a dialog being used (which, since the screen size is so small, is pretty much all of them) causes this issue. On that specific page, the dialog will display fine, but when you select a choice, the dialog closes and leaves you at the page to select from the different form elements, rather than at the demo page you were on.
Note that it seems to be an issue with telling the browser to go back too many times, or in how BB 5.0 handles its history. If you go directly to the page, rather than navigating through the docs & demos site to get there, you'll end up on whatever page you were previously. For instance, if you click the link above on a blackberry 5.0 device, then open a dialog and select a choice, you'll end up back at this issue page.