Strange result of String.fromCharCode

Please could you provide the exact code that gives you the error? I just tried this and it works fine for me with identical firmware on the same device:

>process.env
={
  VERSION: "2v01",
  GIT_COMMIT: "748a4d3",
  BOARD: "ESPRUINOWIFI",
  FLASH: 524288, RAM: 131072,
  SERIAL: "3d002100-0b513532-39333638",
  CONSOLE: "USB",
  MODULES: "Flash,Storage,hea" ... ",neopixel,Wifi,AT",
  EXPTR: 536871128 }
>String.fromCharCode(7)
="\7"