Deduced type from (const) *this used as template function template argument

I have simple class:

#include <utility>

template<class T, class... Ts>
T make(const Ts&... args) //generic class maker
{
    return T(args...);
}

template<class T>
class A
{
public:
    A(void)           : x_(T()), y_(T()) {}
    explicit A(int x) : x_(x), y_(x) {}
    A(int x, int y)   : x_(x), y_(y) {}
    A(const A& other) : x_(other.x_), y_(other.y_) {}
    A(A&& temp)       : x_(std::move(temp.x_)), y_(std::move(temp.y_)) {}

    auto& operator =(A other);
    auto& operator +=(const A& other);
    auto  operator + (const A& other) const;
private:
    T x_;
    T y_;
};

template<class T>
auto& A<T>::operator =(A<T> other)
{
    std::swap(*this, other); return *this;
}

template<class T>
auto& A<T>::operator+=(const A<T>& other)
{
    x_ += other.x_;
    y_ += other.y_;
    return *this;
}

template<class T>
auto A<T>::operator+(const A<T>& other) const
{
    return make<A<T>>(*this) += other;
}

int main()
{
    A<int> first(1);
    auto second = A<int>(2,2);
    auto third  = make<A<int>>(second+first);
    auto fourth = make<A<int>>(4);
    auto fifth  = make<A<int>>(5,5);
}

But when I try to deduce operator+ type from *this, I get strange errors I don't expect:

template<class T>
auto A<T>::operator+(const A<T>& other) const
{
    return make<typename std::remove_cv<decltype(*this)>::type>(*this) += other;
}

int main()
{
    auto solo = A<int>();
    solo + solo;
}

Errors:

error: passing 'const A<int>' as 'this' argument of 'auto& A<T>::operator+=(const A<T>&) 
[with T = int]' discards qualifiers [-fpermissive]
     return make<typename std::remove_cv<decltype(*this)>::type>(*this) += other;
                                                                        ^
error: use of 'auto& A<T>::operator+=(const A<T>&) [with T = int]' before deduction 
of 'auto'
error: invalid use of 'auto'
     return make<typename std::remove_cv<decltype(*this)>::type>(*this) += other;
                                                                           ^
error: invalid use of 'auto'

If I'm right, make(...) should create new object (which should be free of cv), so why do I get discards qualifiers [-fpermissive] error?