Duplicates returned with Table.Distinct in M Query

Hi,

I am trying to create a table containing only distinct rows from the union of two existing Power Query tables in Excel.

My code (anonymised) is:

let
    SelectColumnsT1 = Table.SelectColumns(T1Data,{"Field1", "Field2", "Field3"}),
    SelectColumnsT2 = Table.SelectColumns(T2Data,{"Field1", "Field2", "Field3"}),
    CombineBoth = Table.Combine({SelectColumnsT1 , SelectColumnsT2 }),
    GetDistinct = Table.Distinct(CombineBoth,{"Field1", "Field2", "Field3"})
in
    GetDistinct

Field1 is an integer and the other fields are strings.

This returns duplicates in the resulting table.  I have checked the individual rows which are duplicates and there are no leading/trailing blanks, and when I check within excel that the fields in the duplicated rows are equal, the result is TRUE.

Am I misunderstanding the use of Table.Distinct?

Have I got the syntax wrong?

Is there a bug in this function?

Any other possible things I should look into to try to get to the bottom of this?

I would be grateful if anyone can give me any help on this.

Regards,

Mark