I have heard of bodies moving quite radically after death, usually in a mortuary not a grave. There used to be a curious addition to coffins in times gone - a bell that could be operated from the inside. This was in case someone was about to be buried after only being petrified by illness and not actually dead. A creepy thought.
Yes I have heard of things like scratch marks in the lid of the coffin or other abnormalities. I think this case if different in the fact that they dropped the casket and it over turned causing the thump of the body hitting the lid while the widow and family was there to hear it.