Change of behaviour, or something broke in cin/streambuf behaviour between 3.3.4 and 3.4.1?

[Andrew Walrond]

My application broke between gcc 3.3.4 and gcc 3.4.1 and I don't know quite 
what to make of it.

The code:
  #include <iostream>
  int main(int argc,char* argv[])
  {
          using namespace std;
          std::streamsize a = std::cin.rdbuf()->in_avail();
         cout << " in_avail " << a << endl;
         return 0;
 }
compile with
 gcc -lstdc++ test.cpp
run with
 echo hello | ./a.out

When compiled with gcc 3.3.4 produces

 in_avail 6

but when compiled with gcc 3.4.1 produces

 in_avail 0

Is the code using some undefined behaviour, or did something break?

Andrew Walrond