It turns out that CreateParams
of the parent form has to use the WS_EX_COMPOSITED
flag:
protected override CreateParams CreateParams {
get {
new SecurityPermission(SecurityPermissionFlag.UnmanagedCode).Demand();
CreateParams cp = base.CreateParams;
cp.ExStyle |= 0x02000000; // WS_EX_COMPOSITED
return cp;
}
}