Why does my PictureBox loading routine leak memory?

I've been trying to swap images in a PictureBox in a C++/CLI application but my solution appears to have a memory leak:

System::Void button1_Click(System::Object^  sender, System::EventArgs^  e)
{
    // Pick a new bitmap
    static int resource = IDB_BITMAP1;
    if( resource == IDB_BITMAP2)
    {
        resource = IDB_BITMAP1;
    }
    else
    {
        resource = IDB_BITMAP2;
    }

    // Get the primary module
    Module^ mod = Assembly::GetExecutingAssembly()->GetModules()[0];

    // Get the instance handle 
    IntPtr hinst = Marshal::GetHINSTANCE(mod);

    // Get the bitmap as unmanaged
    HANDLE hbi = LoadImage((HINSTANCE) hinst.ToPointer(),MAKEINTRESOURCE(resource),IMAGE_BITMAP,0,0,LR_DEFAULTCOLOR); 

    // Import the unmanaged bitmap into the managed side 
    Bitmap^ bi = Bitmap::FromHbitmap(IntPtr(hbi)开发者_开发百科);

    // Remove any previously stored images
    if(m_pictureBox1->Image != nullptr)
    {
        delete m_pictureBox1->Image;
        m_pictureBox1->Image = nullptr;
    }

    // Insert the bitmap into the picture box
    m_pictureBox1->Image = bi;

    // Free up the unmanaged bitmap
    DeleteObject(hbi);
}

As far as I can see, I'm explicitely releasing the memory so why does task manager report an ~24k increase in memory each time the button is clicked?

two words: garbage collection

Bizarrely, this actually looks to be caused when you mouse-over the button. Each time you do that the memory jumps but after enough mouse-overs that memory usage stabilises. The actual clicks on the button (i.e. calls to my routine) don't cause any leakage.