sequtils insert produces wrong result in a case of sequence of objects in JS

[pnuzhdin]

import sequtils

type
  Test = object
    a: cstring
    b: int

var test = @[Test(a: "1", b: 1), Test(a: "2", b: 2)]

test.insert(@[Test(a: "3", b: 3)], 0)

echo test

So nim c -r test.nim outputs @[(a: 3, b: 3), (a: 1, b: 1), (a: 2, b: 2)] as expected.
But nim js test.nim outputs @[(a: 3, b: 3), (a: 3, b: 3), (a: 2, b: 2)].

Btw,

import sequtils

var test = @[1, 2]

test.insert(@[3], 0)

echo test

Produces the same result in both cases.

[pnuzhdin]

Can be related to #4139.