Excel not seeing joins

Not sure where the best place to post this question is so trying here first!

I'm using the 'Publish to Excel' add in to connect to a dataset in the Power BI service.

The fact table is joined to a product group table. 

When I build a pivot table using data from the fact table, all is good, however the minute I add a field from the joined table all the fact records appear under all of the possible values from the join table!

Example:

Fact Table

Order 1  Product 1  $100

Order 2  Product 2  $50

Order 3  Product 2  $20

Joined to product group table on Product many to one.

Product Group Table

Product 1   Group 1

Product 2   Group 2

In Power BI I can get:

Group 1  Order 1  Product 1  $100

Group 2  Order 2  Product 2  $50

Group 2  Order 3  Product 2  $20

However in Excel trying to do the same thing I get:

Group 1  Order 1  Product 1  $100

Group 1  Order 2  Product 2  $50

Group 1  Order 3  Product 2  $20

Group 2  Order 1  Product 1  $100

Group 2  Order 2  Product 2  $50

Group 2  Order 3  Product 2  $20

It's as if Excel joesn't see the join and therefore shows all the fact records for each record in the join table?

Any ideas?

Dan