String chunkBySize fails at runtime

[vasily-kirichenko]

open System
"fffff" |> Seq.chunkBySize 3 |> Seq.map String

According to fable.io, it compiles to

import { chunkBySize, map } from "fable-core/Seq";
map(function (arg00) {
  return arg00.join('');
}, chunkBySize(3, "fffff"));

The "Run" button does not work on fable.io, so I cannot test it there, but such code crashes at runtime in my app with

"fffff" |> Seq.chunkBySize 3 |> Seq.map String |> String.concat " " - does not work
"fffff".ToCharArray() |> Array.chunkBySize 3 |> Array.map String |> String.concat " " - works

In F# REPL both ^^ return the same value "fff ff".