The Doors

The front door to every apartment on the sixth floor was gone.
Nothing else had been stolen, nothing else had been disturbed.
Nobody heard or saw anything out of the ordinary.
The security cameras in the stairwells, elevators, garage, and lobby showed nothing strange.
One moment, the doors were all there.
The next moment, they were gone.
Why would somebody steal all the doors on the sixth floor?
They were just ordinary doors.
And why chose that floor?
Why not the fifth? Or the seventh?
The next day, they were back.
Nobody said a thing about it.
Was I dreaming?