Here is the test code:

    typedef struct
    {
        int ele;
    } tstruct;

    #define TST(r,t) r##t = 1

    void test()
    {
        tstruct ts;

        TST(ts,.ele);
    }

It generates the error:

    "error: pasting "ts" and "." does not give a valid preprocessing token"

In previous versions of compiler (eg gcc-3.2.2) this generated a warning and could therefore be ignored as another piece of unhelpful compiler output.  But now it is a error (but it isn't!) which stops compilation.