Clang: Highlighting of argument to user defined index operator is wrong

struct Foo {
    Foo &operator[](int key);
};

void failsHere()
{
    const int index = 3;
    Foo foo;
    foo[index]; // Ops, "index" is highlighted as "function"
}

void worksAsExpectedHere()
{
    const int index = 3;
    int foo[100];
    foo[index]; // OK, "index" is highlighted as "local variable".
}