Power Query duplicates data

Before data can be loaded into Power BI, they have been transformed and modified with Excel’s Power Query. I have two sets of data. After transforming them, they have the same structure and same column header. To reach this point, I used the following mapping table to assign each Entity a certain Country. Normally there is a 1:1 match, except for those entities below.

To combine both data sets, I have used

= Table.Combine({data_set_1, data_set_2})

in Excel’s Power Query Editor.

The result astonishes me: For the countries above (Coration, Czech, Hungary, Lebanon) the data of data_set_1 have been duplicated! All other countries are fine (which are not on the list above and which had a 1:1 relationship). However, I haven’t linked the mapping table as a reference to the newly created combined table in “Manage Data Model”. Data_set1 and data_set_2 have been double checked before the have been combined and they don’t contain any duplicated rows.

My question is: Why is Power Query using a mapping table although it has not been instructed to do so? How can I “switch” of this unintended function?

Any hints and comments are highly appreciated.

Thanks, Carsten