Update Datasources doesn't work with merge queries in model

The new Update Datasources REST API is great but doesn't work if an imported table contains a merge queries step to join to another table.

• The call to /updatedatasources returns success
• The call to /BindToGateway returns success, using a gateway with a data source for the new DB server/database
• The refresh fails with "Invalid connection credentials.". The underlying error message indicates that the original server/database values are being used.

I have reproduced with a couple of test tables and two PBIX files: one includes a merge and the other doesn't.