Behavior of deleting object properties in a loop differs from browser JavaScript runtimes

Run this snippet in qmlscene:

import QtQuick 2.0

Item {
  Component.onCompleted: {
    var obj = {foo: 1, bar: 2, asdf: 3, blub: 4};
    console.log("before: ", JSON.stringify(obj));
    for (var prop in obj) {
      delete obj[prop];
    }
    console.log("after: ", JSON.stringify(obj));
  }
}

expected output:
qml: before:

qml: after: {}

actual output:
qml: before:

qml: after:

When you run the snippet above (i.e. the contents of Component.onCompleted) in a browser environment (WebKit, Chromium, ...), the expected output will be shown.