? Bug in libstdc++? GCC 4.1: wcout.imbue(loc) should (?) set stream encoder's, but it doesn't; std::locale::global() shouldn't change it, but it does?

There was the same topic not so long ago, but as I see it stays w/o
answer:
http://groups.google.ru/group/comp.lang.c++/browse_thread/thread/9a05d7bba9394a60/fe109c899f916871?lnk=gst&q=locale+imbue&rnum=1&hl=ru#fe109c899f916871

As Bjarne Stroustrup said in his book,
"in Stroustrup (retranslated from German)
"Setting the global locale does not affect existing input/output
streams. The streams continue to use those locales that were assigned
to
them using imbue() during their creation." "

But actually I see quite the opposite behaviour.
The following code:

  #include <iostream>
  // #include <clocale>
  #include <locale>

  int main() {
    std::locale loc("") ;
    // std::setlocale(LC_ALL, "") ; // (1)
    std::locale::global(loc) ; // (2)
    // std::wcout.imbue(loc) ; // (3)
    std::wcout << L"(non-ASCII national letters here)" << std::endl ;

    std::wstring wstr ;
    std::wcin >> wstr ;
    std::wcout << L'[' << wstr << L']' << std::endl ;

    return 0 ;
  }

DOES work (it correctly inputs and outputs non-ASCII, non-"C"-locale
chars), while it SHOULD NOT (?), and if you commented out (1) and (2)
and uncommented (3) - it DOESN'T work, though it SHOULD DO (as
Stroustrup says).

More over, if you switch global locale between points of wcout usage,
like:

  int main() {
    std::locale loc("") ;
    std::wcout << L"(non-ASCII national letters here)" << std::endl ;
    std::locale::global(loc) ; // (2)
    std::wcout << L"(non-ASCII national letters here)" << std::endl ;

- wcout DOESN'T WORK correctly even after global locale switch!!!

What's wrong with my attempts to make it work??

(I'm afraid, it's one more of numerous problems/bugs of C/C++
alliance, but would happy to hear "official" answer and ways to
workaround...)