Possible bug with Storage.open

Hi there!

Before opening a bug on the tracker, I wanted to double check this behaviour.
This code opens a file in append mode, and writes some text in it.

const Storage = require('Storage')
const name = 'test'
Storage.erase(name)
const file = Storage.open(name, 'a')
console.log('-> files', Storage.list())
// file not in the list
file.write('whatever')
console.log('-> files', Storage.list())
// file exists, but has a \1 octal escape sequence appended to its name

this gives:

 ____                 _
|  __|___ ___ ___ _ _|_|___ ___
|  __|_ -| . |  _| | | |   | . |
|____|___|  _|_| |___|_|_|_|___|
         |_| espruino.com
 2v04 (c) 2019 G.Williams
>-> files [
  "+mclock",
  "-mclock",
  "*mclock",
  "+setting",
  "-setting",
  "=setting",
  "*setting",
  "+sbt",
  "=sbt",
  "+sbat",
  "=sbat",
  "+files",
  "-files",
  "*files",
  ".trishig",
  ".bootcde",
  "@setting",
 ]
-> files [
  "+mclock",
  "-mclock",
  "*mclock",
  "+setting",
  "-setting",
  "=setting",
  "*setting",
  "+sbt",
  "=sbt",
  "+sbat",
  "=sbat",
  "+files",
  "-files",
  "*files",
  ".trishig",
  ".bootcde",
  "@setting",
  "test\1"
 ]

This \1 at the end: is it expected?