RowIndex calculated wrongly?

I just stumbled across something what i think is a bug. In the preview the RowIndex in a column Expression node for the first row is 0:

Later in the output table it is 1:

Has something changed/gotten ouf order with an update? I looked up an old documentation (of mine) where the screenshot looks like:

I can not say from when exactly the screenshot is nor what thenode was - it’s cut of on top and i don’t remember.

i realized this today because 1 table was 1 row shorter tahn i expected.