The following code issues an incorrect warning.
Note, that the non-template version (fine) is fine.

gonzo:/tmp # cat foo.cc
template <class T>
void foo(T &a)
{
  for(int i = 0, j = 0; i != 3; ++i, ++j)
    a += j;
}

void fine(int &a)
{
  for(int i = 0, j = 0; i != 3; ++i, ++j)
    a += j;
}

int
main()
{
  return 0;
}

gonzo:/tmp # /gml/shared/gcc-cvs/bin/g++ -v
Reading specs from /gml/shared/gcc-cvs/lib/gcc-lib/i686-pc-linux-gnu/3.4/specs
Konfiguriert mit: ../gcc/configure --prefix=/gml/shared/gcc-cvs --enable-shared
--enable-languages=c,c++ --enable-threads=posix
Thread model: posix
gcc-Version 3.4 20030726 (experimental)

gonzo:/tmp # /gml/shared/gcc-cvs/bin/g++ -Wunused-value foo.cc
foo.cc: In function `void foo(T&)':
foo.cc:4: Warnung: left-hand operand of comma expression has no effect