Duplicate, named dogs

On "Peaceful," logged in (very slow) to void & entities. World began loading; heard my named dog barking &midnight music start then stop midway. Heard another dog yelp, take fall damage. 2nd dog approached me: same dyed collar, same name; followed me. Logged out; logged in; 2nd dog still there. Able to breed duplicate dogs; have puppy. Also: some named testificates & chickens have disappeared. Began recording video within 10 seconds of initial sighting of 2nd dog. http://youtu.be/hvBWCO5kgnY