Currently the RI allows to mark a method return value with @Valid, also if the overridden/implemented method from the supertype or interface respectively is already marked with @Valid.

According to the latest spec draft this is not allowed (section 4.5.5):

One must not mark a method return value for cascaded validation more than once in a class hierarchy. In other words, sub types (be it sub classes/interfaces or interface implementations) cannot mark the return value for cascaded validation if the return value has already been marked on a super type or interface.