The Los Angeles Times
reports that the first Mickey Mouse cartoons have ambiguous copyright claims, listing two other potential claimants between "Disney" and the word "copyright". Under interpretation of the law at the time, this does not constitute a proper copyright claim.
Given that previous copyright rulings against Disney were unsuccessful on the basis of the existence of previous copyright claims, and these claims now appear not to be valid, this is significant news to one of the biggest beneficiaries of copyright laws.