Exactly Anne there too many contradictions about the shutters. They were found to be a good alibi for one person when he was in fact out searching with the other men. If that person went past the Smith family you can bet that he would want an alibi for that time and the embellished story about wasting precious time in examining the shutters like a CSI officer instead of looking for Madeleine became it. As you point out Dianne was examining them only minutes later when Kate was found alone in the apartment. That's the important part the false alibi.
If Mrs McCann had told Mrs Webster "Gerry has already checked it, Dianne, those shutters can be lifted from the outside", why would Mrs Webster have tried herself ?
I always found it was too much, even for a pragmatic doctor, to manipulate shutters a few minutes after discovering his daughter is missing,
Mr McCann learnt a bit about this kind of shutters when he messed his bedroom's ones.
There was an obvious reason, though it made Mr McCann appear an extraordinary cold blood father, to claim he experimented the shutters and was amazed they were liftable from the outside : the planet had to believe the intrusion through window. And in fact it did.
But Mr McCann didn't touch the shutters, he had other things to do.
