Version:            (using KDE KDE 3.4.0)
Installed from:    Debian testing/unstable Packages
OS:                Linux

kdelibs source contains code of this form:
     
    namespace NS1 {
        struct S {
            int foo();
        };
    }
     
    using namespace NS1;
     
    namespace NS2 {
        int S::foo() { return 0; }
    }

(Specifically, KNetwork::internal.)

This is illegal C++, though gcc 3.4 allows it due to a bug:
    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20711

Other compilers such as Intel C++ reject this.