Consider the following code snippet:

struct S {
    union  {
        int i = 12;
        void *something;
    };
    int func(bool b) {
        if (b)
            return i; // <-- here
        int i = 42;
        return i;
    }
};

In the marked line, i is not colored as a member variable; moreover go-to-definition will jump to the local definition of i, instead of to the one inside the union.

If the union is replaced with a simple member i, or if this->i is used instead of i, everything works as expected.