Extended Analytics data extract - update star schema 'replaces' data

I read that when choosing 'update star schema' when extracting data using Extended Analytics, it 'appends' the data to the data already in the destination database. Our testing shows that it seems to be 'replacing ' the data based on entity. If there was data in the database for a given entity in a given account, and then we used update star schema to extract a second account for that same entity, the database holds the second accounts data for that entity, and clears the original account data extracted. This is not an append.

What do we have to do to get the 'append' functionality to work?