node 0.8.11 stdout/stderr setEncoding('utf8') strangeness

gistfile1.js

var assert = require('assert')
var spawn = require('child_process').spawn


function runTest(cb) {
  var proc = spawn("/usr/bin/env", [], {env:{foo:"bar"}})

  proc.stdoutBuf = ""
  proc.stderrBuf = ""
  proc.stdmergedBuf = ""

  proc.stdout.on('data', function(buf) {
    proc.stdoutBuf += buf
    proc.stdmergedBuf += buf
  })

  proc.stderr.on('data', function(buf) {
    proc.stderrBuf += buf
    proc.stdmergedBuf += buf
  })

  proc.on('exit', function(exitCode) {
    assert.notEqual(proc.stdoutBuf.length, 0, "proc.stdoutBuf has length 0!")
    if (cb) cb()
  })

  return proc
}

var proc1 = runTest(function() {
  console.log("completed test without utf8-encoding")
  var proc2 = runTest()
  proc2.stdout.setEncoding('utf8')
  proc2.stderr.setEncoding('utf8')
})