Why is there a difference between an operator and the corresponding member function?

Why is there a difference between the operator call and the corresponding member function call with Clang 17.0.1? Shouldn't they behave the same way?

#include <iostream>
    
struct A {
    void operator()(int) { std::cout << "A...\n"; }
};

struct B {
    void operator()(double) { std::cout << "B...\n"; }
};

template<typename... Ts> struct C : Ts... {};

int main() {
    C<A, B> c;
    c(1);
    c.operator()(1);
}

Compiler Explorer

The call

c(1);

works, but the call

c.operator()(1);

produces the error message

error: member 'operator()' found in multiple base classes of different types

The error message is clear. I was surprised that c(1) doesn't produce this error.

The call c(1); works,

This seems to be a fixed clang 17.0.1 bug. Both calls are equivalent and produces the same error in the latest version of the clang etc.