Debug a std::unique_ptr with custom deleter fails

#include <iostream>
#include <memory>

// The most basic deleter
template <typename Allocator>
struct deleter {
    Allocator allocator;
    deleter() :
            allocator() {
    }
    deleter(Allocator& allocator) :
            allocator(allocator) {
    }
    void operator()(typename std::allocator_traits<Allocator>::value_type* ptr) {
        std::allocator_traits<Allocator>::destroy(allocator, ptr);
        std::allocator_traits<Allocator>::deallocate(allocator, ptr, 1);
    }
};

// A function that allocates and constructrs (using args) a value and returns a unique_ptr pointing to
template <typename Allocator, typename... Args>
std::unique_ptr<typename std::allocator_traits<Allocator>::value_type, deleter<Allocator>>
allocate(Allocator& allocator, Args&&... args) {
    auto* ptr = std::allocator_traits<Allocator>::allocate(allocator, 1);
    std::allocator_traits<Allocator>::construct(allocator, ptr, std::forward<Args>(args)...);
    return {ptr, deleter(allocator)};
}

int main() {
    std::allocator<int> al;
    std::unique_ptr<int> a(allocate(al, 123456).release());                               // Case 1
    std::unique_ptr<int, deleter<std::allocator<int>>> b(allocate(al, 123456).release()); // Case 2
    std::cout << "a: " << *a << std::endl;
    std::cout << "b: " << *b << std::endl;
    return 0;
}