Странное поведение CreateWindowEx

#include "stdafx.h"
 
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
 
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE prevInst, LPSTR lpCmdLine, int nCmdShow)
{
    HWND hMainWnd = NULL;
    TCHAR wndClassName[] = L"MainWndClassName";
    MSG message;
 
    WNDCLASSEX wndClass;
    ZeroMemory(&wndClass, sizeof(wndClass));
 
    wndClass.cbSize        = sizeof(wndClass);
    wndClass.hInstance     = hInst;
    wndClass.lpfnWndProc   = WndProc;
    wndClass.lpszClassName = wndClassName;
    wndClass.style         = CS_HREDRAW | CS_VREDRAW;
    wndClass.cbClsExtra    = NULL;
    wndClass.cbWndExtra    = NULL;
    wndClass.lpszMenuName  = MAKEINTRESOURCE(IDR_MENU);
    wndClass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
 
    if (!RegisterClassEx(&wndClass))
    {
        MessageBox(NULL, L"wndClass not registret", L"ERROR", MB_OK);
        return 1;
    }
 
    hMainWnd = CreateWindowEx(NULL, wndClassName, L"DevelopEx Final Test", WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT, NULL, CW_USEDEFAULT, NULL, NULL, NULL, hInst, NULL);
    if (!hMainWnd)
    {
        MessageBox(NULL, L"hMainWnd window not create", L"Error", MB_OK);
        return 2;
    }
 
    ShowWindow(hMainWnd, nCmdShow);
    UpdateWindow(hMainWnd);
 
    while (GetMessage(&message, NULL, NULL, NULL))
    {
        TranslateMessage(&message);
        DispatchMessage(&message);
    }
 
    return message.wParam;
}
 
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_DESTROY: {
        PostQuitMessage(NULL);
        break;
    }
    default:
        DefWindowProc(hWnd, uMsg, wParam, lParam);
    }
 
    return NULL;
}

wndClass.lpszMenuName = NULL;

default:
        return DefWindowProc(hWnd, uMsg, wParam, lParam);