I'm running into the same problem. The July version (v2011.2 712) works, but the September one (v2011.2 920) doesn't. I'm still on the SL 5 beta because I had too many issues with SL 5 RC. Looking at the change notes for 920, there were two bug fixes for RadDataPager.
- Fixed: DataPagerAutomationPeer GetChildren().
- Fixed: RadDataPager does not properly dispose its PagedSource.