ModifyStyle to gray out maximize-button leads to disappearing button

Question

I have a small application, where you can set, if maximize or minimize button is active or not/grayed out.

if (!m_bActiveMaximizeButton)  // Maximieren
{
    this->ModifyStyle(WS_CAPTION|WS_MAXIMIZEBOX,0,0);
    this->ModifyStyle(0,WS_CAPTION,SWP_FRAMECHANGED);       
} else
{
    this->ModifyStyle(WS_CAPTION,0,0);
    this->ModifyStyle(0,WS_CAPTION,SWP_FRAMECHANGED);
}
if (!m_bActiveMinimizeButton)   // Minimieren
{
    this->ModifyStyle(WS_CAPTION|WS_MINIMIZEBOX,0,0);
    this->ModifyStyle(0,WS_CAPTION,SWP_FRAMECHANGED);
} else
{
    this->ModifyStyle(WS_CAPTION,0,0);
    this->ModifyStyle(0,WS_CAPTION,SWP_FRAMECHANGED);
}
    CMenu* menue = this->GetSystemMenu(FALSE);

if (!m_bActiveCloseButton)  // Schließen X
{
    menue->ModifyMenu(SC_CLOSE, MF_BYCOMMAND | MF_GRAYED);
} else
{
    menue->ModifyMenu(SC_CLOSE, static_cast<UINT>(MF_BYCOMMAND | ~MF_GRAYED));
}

This works fine with Windows 7 styles. However, with Windows 10 styles, the buttons do not gray out, but they disappear completely. Deactivating the "Close" button does not work at all anymore.

What do I have to change to gray out the buttons again?