The static member map variable address is changed evertime returned by get function when linking against a static library

I meet a strange problem. When I build my sources into a dynamic library, everything works fine, I can get expected result, but when I instead building into a static library, some wrong happens, yet I don't know why.

I want to implement a factory class that can create a specific class instance by its name in string format.

Minimum codes for demonstration:

factory.h

#ifndef _FACTORY_H
#define _FACTORY_H

#include 


class SomeClass;

class Factory
{
  typedef std::map<std::string, SomeClass*(*)()> mapType;
public:
  static SomeClass * CreateInstance(const std::string &className);

protected:
  static mapType * getMap();

private:
  static mapType * _constructorMap;
};

template<typename T>
SomeClass * createSomeClass()
{
  return new T;
}

template<typename T>
class FactoryRegister : Factory
{
public:
  FactoryRegister(const std::string &name)
  {
    getMap()->insert(std::make_pair(name, &createSomeClass));
  }
};

#define REGISTER_DEF_TYPE(NAME) 
    FactoryRegister NAME::regTbl(#NAME)

#define ADD_REGISTER_TABLE(NAME) 
    static FactoryRegister regTbl


#endif // _FACTORY_H

factory.cpp

#include 

#include "factory.h"

Factory::mapType * Factory::_constructorMap = nullptr;
SomeClass * Factory::CreateInstance(const std::string &className)
{
  mapType::iterator it = getMap()->find(className);
  if(it == getMap()->end())
  {
    qWarning("Construct %s failed. Not find a construct in map.", className.c_str());
    return nullptr;
  }
  return it->second();
}

Factory::mapType * Factory::getMap()
{
  // never delete'ed. (exist until program termination)
  // because we can't guarantee correct destruction order
  if(!_constructorMap)
  {
    _constructorMap = new mapType;
  }
  return _constructorMap;
}

Until now, I can build factory source file into library, dynamic library or static library, say it libfactory.so or libfactory.a. And it will be linked with user codes, like SubClassA, SubClassB or any other sub-classes derived from SomeClass:

// SubClassA.h
class SubClassA: public SomeClass
{
  ADD_REGISTER_TABLE(SubClassA);
}

// SubClassA.cpp
REGISTER_DEF_TYPE(SubClassA);

Everything works fine when linking libfactory.so, that is I can create SubClassA instances. But it won't work when linking libfactory.a. As I know, the only difference is just the build library type.Below is the error print:

Construct SubClassA failed. Not find a construct in map

Besides, I found when linking against a static library, the mapType * getMap() will always return different pointers, that really a weird thing.

Any ideas? Appreciate for that.