Hallo,
Ich vermute das ist in alen Browsern so?
Jedenfalls ist das ein notwendiges Erfordernis an jede ECMAScript-Implementation:
»When you reference a property or method of a string value, the ECMAScript engine must implicitly create a new string object with the same value as your string, before running the method. This object is only used for that one request, and will be recreated next time you attempt to use a method of the string value.«
Mathias