Google Sheets Append New Row(s) Bug?

In our app, when we "Append Data to a Spreadsheet" and give it an object with each matching column it appends them to the next blank row - but it starts at the column AFTER.

Example:

Sheet has data in columns A10 to C10

If we submit data we want in A11, B11, C11, they will get added on D11, E11, F11 for some reason.

Is this a known issue?