Improper std::pmr::polymorphic_allocator not detected at compilation time

Question

I found that the pmr::polymorphic_allocator type seems to be not properly detected at compilation type.

I've the class (for example MyClass), what uses pmr::polymorphic_allocator, and this allocator has to be passed by constructor parameter:

// file MyClass.hpp
#include <memory_resource>

class Item
{
    // class members...
};

class MyClass
{
public:
    explicit MyClass(std::pmr::polymorphic_allocator<Item> allocator)
    {
        // ....
    }

    // other members
};

Then, I'm trying to use my class:

#include "MyClass.hpp"
#include <memory_resource>

// this compiles w/out errors - as expected
auto myClass1 = MyClass(std::pmr::polymorphic_allocator<Item>());

// and this compiles w/out errors too - as NOT expected
auto myClass2 = MyClass(std::pmr::polymorphic_allocator<OtherType>());

Off course, the type OtherType is totally different than type Item.

So, I added some additional checks in constructor of MyClass:

// file MyClass.hpp
#include <memory_resource>
#include <type_traits>

class Item
{
    // class members...
};

class MyClass
{
public:
    explicit MyClass(std::pmr::polymorphic_allocator<Item> allocator)
    {
        static_assert(std::is_same<Item, decltype(allocator)::value_type>::value,
            "Improper allocator!"); 
        // ....
    }

    // other members
};

... and the improper allocator is still not detected. I can't find any reason for that. Any ideas?

My environment: GCC 10.2.0, CLion 2021.1

EDIT: ok, I found the reason. The pmr::polymorphic_allocator has converting constructor, so there occurs the implicit conversion to the expected allocator: constructor description on cppreference.com. So, it seems that there is no way to detect the usage of improper allocator.