C++ Win API window mouse busy on x64 platform

Question

I created in C++ a window with the Win API.
If I set the target platform to x86 in Visual Studio (2015) all works fine.
But if I set the target platform to x64 all works fine too except that I get a busy cursor for the first 4-5 seconds when the window popped up.
This isn't that bad but I am just wondering what is causing this.
I saw this behavior when using GLFW too so it seems to be not a programming error.

Maybe someone know what is causing this?

#include <windows.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_DESTROY:
    {
        PostQuitMessage(0);
        return 0;
    }
    break;
    }

    return DefWindowProc(hWnd, message, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    HWND hWnd;
    WNDCLASSEX wc;

    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = NULL;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
    wc.lpszMenuName = NULL;
    wc.lpszClassName = "MainWindowClass";
    wc.hIconSm = NULL;

    RegisterClassEx(&wc);

    RECT wr = { 0, 0, 800, 800 };
    AdjustWindowRectEx(&wr, WS_OVERLAPPEDWINDOW, FALSE, 0);

    hWnd = CreateWindowEx(0, "MainWindowClass", "DirectX Lab", WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, wr.right - wr.left, wr.bottom - wr.top, NULL, NULL, hInstance, NULL);

    ShowWindow(hWnd, nCmdShow);

    MSG msg;

    while (GetMessage(&msg, NULL, 0, 0) != 0)
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam;
}