Your reasoning is perfect, Benice, but it requires 1) believing the McCanns about the state of the window/shutters and 2) forgetting that they were in such a terrible emotional state that they couldn't possibly stage anything.
But how could a couple who were so cold hearted and unmoved by the death of their daughter that they were capable of disposing of her body like a sack of old rubbish, not be able to just as coldly sit down and work out what they were going to say about the shutters/window - which after all was going to be the proof that an abductor had broken in and was in fact the most important part of their plan.
Surely such people would not be panicking at all at the planning stage - why would they be? and they certainly would not have overlooked the fact during that discussion that at least some evidence needed to be present to prove a break in. So why didn't these cunning criminal masterminds provide some in readiness for the obvious inspection of the window by the PJ which they knew would take place?
Obviously I don't believe for one moment that any of the above happened, which is why I believe Kate told the truth when she said the shutters were up and the window was wide open when she found Madeleine missing and this led her to immediately believe that an abductor had broken in and taken her daughter. And that is when the nightmare started.