Custom dwm drawn window frame flickers on resizing if the window contains a HwndHost element

Well, I finally found a fix but I think this one borders on black magic... anyway it turns out that responding to WM_NCCALCSIZE with any rect smaller than the window solves the problem.So for example changing the handler to look like below removes the flicker!

            case WM.NCCALCSIZE:                if( wParam != IntPtr.Zero ) {                    handled = true;                    var client = (RECT)Marshal.PtrToStructure( lParam, typeof( RECT ) );                    client.Bottom -= 1;                    Marshal.StructureToPtr( client, lParam, false );                }                break;

I have no idea why this is working and I'm sure that a saner solution exists, so I'd be happy if someone could enlighten me.

I solved it by adding WS_CLIPCHILDREN as a style when CreatWindowEx

protected override HandleRef BuildWindowCore(HandleRef hwndParent){    _hwndHost = Win32Api.CreateWindowEx(0, "Static", "",                         (int) (WS_CHILD | WS_VISIBLE | WS_CLIPCHILDREN),                      0, 0,                      _hostWidth, _hostHeight,                      hwndParent.Handle,                      IntPtr.Zero,                      IntPtr.Zero,                      0); }