no, there's no way police would be allowed to issue false info under any circumstances. They can withhold info, but cannot issue false info because it could jeopardise any trial.
Imagine police issue photofit of man seen in cafe with child resembling Madeleine, DNA is taken and it is confirmed that the child was Madeleine, but the police don't want the man to be freaked so they say that the DNA wasn't her's. So eventually this man is caught, only he doesn't have Madeleine with him, but he's the same man seen in the cafe, so he's charged in connection with the abduction. Then the case comes to trial, and immediately the defence produce... "statement from police saying that DNA found on the bottle was not Madeleine's". So no evidence to link the man to the child, in fact the police have gone on record saying the child wasn't there.
If the police say the DNA on the bottle wasn't Madeleine's, then the DNA wasn't Madeleine's.