Memory leaks using shared_mutex

Question

The following code leads into an increasing usage of memory:

#include <shared_mutex>

class foo
{
public:
   void bar()
   {
      std::unique_lock lock(m_mtx);
   }
   std::shared_mutex m_mtx;
};

int main()
{
   while (1)
   {
      foo obj;
      obj.bar();
   }
}

The following do not: (only changes the mutex type)

#include <mutex>

class foo
{
public:
   void bar()
   {
      std::unique_lock lock(m_mtx);
   }
   std::mutex m_mtx;
};

int main()
{
   while (1)
   {
      foo obj;
      obj.bar();
   }
}

I am using Windows 7 and using the task manager to track the memory consumption of my program.

I compile with mingw and this simple command line to compile:

g++.exe -std=c++17 -o mytest main.cpp

What i am doing wrong with the usage of shared_mutex ?