Hi,
Many significant changes have been made since Beta 1 in relation to the creation of Tile Packages in ArcGIS Desktop and how we read Tile Packages in the ArcGIS Runtime SDK for WPF.
I can confirm that this the TPK you refer to on ArcGIS.com can be read fine with the current API so it would appear that whatever the issue was, it has been resolved.
We really appreciate your feedback.
Cheers
Mike