This is expected as merging currently requires a header row for each file so that it can automatically line up the data accurately.

For example if you had two csv files...

[File1.csv]

    Id,ProductId
    1,200
    2,300

[File2.csv]

    ProductId,Name,Id
    400,NameFor400,3
    500,NameFor500,4

Final output would be...

[Output.csv]

    Id,ProductId,Name
    1,200,""
    2,300,""
    3,400,NameFor400
    4,500,NameFor500

With that said, thanks for commenting! I will add an option for "No Header" files, or maybe even auto detect for these situations and do a straight merge:)