Clang code model: False unused-function warning

The clang code model highlights a function in the editor with an unused-function warning although the function is used when compiling the code.

I think the problem is somehow related to the way qt creator parses multiple files, because it can only be reproduced, if certain conditions are met. See my sample code:

#include <stdio.h>

/// In a header file
struct S {};

template <typename T>
const S &operator<<(const S &s, const T &l)
{
	return s << l;
}
/// In a cpp file

int main()
{
	S() << 0;
}

static const S &operator<<(const S &s, int x) {
	(void) x;
	printf("operator<<(const S &, int)\n");
	return s;
}

The warning is emitted for const S &operator<<(const S &s, int x).
If either the declaration of struct S or of the template is moved to the cpp file, no warning is emitted. In both cases the code compiles just fine with all compilers i've tested.

I am not really sure if the code is even valid c++, because the operator<<(S,int) should not be visible to the template operator. If I change it to a normal function, it does in fact not compile (at least with gcc  4.8.7, but msvc2017 compiles). Adding a declaration for the non template operator between the declaration of the struct and the template operator removes the warning.

Still I think it is a bug and it may have other consequences, because the code compiles just fine, even with the clang version shipped together with the creator