C++ Win API window mouse busy on x64 platform - c++

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;
}