sheet_add_json with origin: -1 leaves gap from bottom of worksheet

I’m seeing strange behavior with the following code:

const XLSX = require('xlsx');

const wb = XLSX.utils.book_new();

const ws = XLSX.utils.json_to_sheet([
  { Product: 'p2', Qty: 2 },
]);

XLSX.utils.sheet_add_json(ws,
  [
    { Product: 'p3', Qty: 3 },
    { Product: 'p4', Qty: 4 },
    { Product: 'p5', Qty: 5 },
    { Product: 'p6', Qty: 6 },
    { Product: 'p7', Qty: 7 },
    { Product: 'p8', Qty: 8 },
  ],
  {
    header: ['Product', 'Qty'],
    skipHeader: true,
    origin: -1,  // append to bottom of worksheet starting on first column
  }
);


XLSX.utils.book_append_sheet(wb, ws, 'Bug sheet');

XLSX.writeFile(wb, 'bug.ods');

I expected p3…p8 to be placed on rows 3 … 8, but they ended up on rows 6 … 11 (in LibreCalc at least).

I’m on 0.14.1. What might be going on?

[dandv]

Greetings from 2021 ❗

[dandv]

Here’s a 2020 ping!