Methods and apparatus for a video coding system with the current picture referencing (CPR) mode enabled are disclosed. According to one method, when the current reference picture is equal to the current picture, an integer motion vector flag is inferred to be true without signalling the integer or parsing the motion vector flag. In another method, when all motion vector differences for the current block are equal to zero, an integer motion vector flag is inferred to be true without signalling the integer or parsing the motion vector flag. In yet another method, when all reference pictures for the current block are equal to the current picture: the sub-block prediction coding mode is disabled; and the current block is encoded or decoded by disabling the sub-block prediction coding mode. Alternatively, derived motion vectors associated with sub-blocks for the current block can be converted into integer motion vectors.