Change Data Source Causes Error with Relationships on identical DB

Hi,

For the past few months I've been using the "Change Data Source" option to switch between test and prod databases. But this morning I started receiving the below error essage on all relatinoships when changing the source:

Failed to save modifications to the server. Error Returned: 'Relationship '...' between columns '...' and '...' cannot be created becuase they are not from the same DirectQuery data source. 

The two DB's are identical and when I remove the relationships change data source is successful and then I have to manually add the relationships back. 

Is this a bug in Desktop? Any ideas on what the issue may be?