Which dogs are you talking about and what time of day was it?
If it is the tracker dogs, since that unit seems to have arrived around 11pm, I would assume the issues with 5J were no key (got round by access from a neighbour via the rear balcony and patio doors) and the time of night.
The immediate priority with the dogs seemed to be searching the environs and checking out possible areas Madeleine could have accessed had she been moving under her own volition.
I think that was probably the logical thing to do as that was in line with their training.
It was only when she was not found outside, which I think may have been the expectation, that closer attention was given to what might happen within the apartment blocks if the dogs were given free rein there.
I think the interest in what we are told was an unoccupied property (5J) merited immediate attention and forensic examination, rather than acceptance that an open fridge door and rotting food explained the dogs' reaction.
**snip
7th May
At about 23.00 accompanied by a PJ inspector, the searches were begun. After Rex was given the girl's clothing to sniff, he began to search on the ground floor of block 5 and when he passed the door of apartment 5 A (the place the girl had disappeared from) according to his handler, officer Fernandes, the dog altered its behaviour, sniffing with greater intensity than he had done before. Apartment 5J of the same block was also checked as the dog had been more agitated than before as if there were a very strong strange odour there. It was stated that this apartment had been unoccupied for some time. Afterwards, the same kind of search was carried out using the dog Zarus which in general terms showed the same behaviour in the same places as Rex had done.
It was only when all the searches of the apartments in blocks 4 and 5 were complete, that the behaviour described above was registered. It is certain that this kind of work does not correspond to the area that these dogs were trained in, but given that these types of dogs manage to discriminate a specific odour from others, although it could be a remote possibility that they related the odour of the missing girl with a possible location where she could have been.
**snip
On 10th May at about 20.10, upon the request of the PJ, searches were carried out in all of the apartments belonging to blocks 4 and 5 of the OC, two tracker dogs and two search and rescue dogs being used for this operation, adopting the same methods as those used on 7th May, just that this time the apartments were all open and searched one by one, being accompanied by a representative from the resort, who had the keys to all the apartments (apart from those not under her administration) and also with the objective of helping with the searches. The collaboration of all the guests occupying the apartments at that time was requested for this purpose and those apartments that were found to be empty were opened by the administrator.
http://www.mccannpjfiles.co.uk/PJ/GNR_SNIFFER.htm