If QFileDialog::getOpenFileName() is called in a button click event or other event, a dependent DLL will not unload

If I use QFileDialog::getOpenFileName(this), a dependent DLL will not unload. For example, assume there are two projects:

1. Exe Project (Qt project)
2. DLL Project, used by the Exe Project (implicitly linked)

If the Exe Project uses the QFileDialog::getOpenFileName() in button click event or other event, the DLL will not unload.

BOOL WINAPI DllMain(
  _In_  HINSTANCE hinstDLL,
  _In_  DWORD fdwReason,
  _In_  LPVOID lpvReserved
)
{
	if (fdwReason == DLL_PROCESS_ATTACH)
	{
		//Load lib
		int x = 100;
	}
	if (fdwReason == DLL_PROCESS_DETACH)
	{
		//UnLoad lib here not call when colse
		int x = 100;
	}
	return TRUE;
}

And the DLL global var will not be destroyed.

I've posted this problem in the forums: https://qt-project.org/forums/viewthread/40575/

I've attached a test case.

Thanks in advance.