Yes there is
You dont need a key to open an unlocked door from the inside...please remind yourself of the title of this thread!
The objective of having a lock on a door is to deny non-keyholders or intruders entry to the interior. Therefore, the shutter being down and the front door closed and requiring a key to open it ... the Drs McCann thought the front of the apartment secure from petty thieves.
They did not know about the assaults which had been perpetrated on British children in their beds, so that did not enter their thinking.
It did not occur to them that an abductor might be on the loose, so didn't give that a moment's thought either.
It is unlikely however that Madeleine would have been able to effect an exit through the door without leaving a forensic trace on the door or on the wall.
Do we know if the door was dusted for fingerprints?
Mark Williams-Thomas considered the woke and wandered theory; he also considered the comparisons of the disappearance of another little girl which he was able to do without prejudice.
Which was something the team leaders of the original investigation were prevented from considering. To do so would have questioned the conviction of Leonor Cipriano for her missing daughter's murder.
Many of the investigating officers in Joana's case were also investigating Madeleine's.
Therefore it is wrong to say all avenues were open to investigation from the start if investigation of the connection between both cases was not considered particularly as an experienced professional like MWT thought it relevant to do so.
The team responsible for 'solving' Joana's case could scarcely afford to link her's to Madeleine's disappearance even if only for elimination purposes without prejudice to what had gone before.