UICollectionView：isDragging属性未处于正确状态

I have full-screen UICollectionView cells (first-left -> last-right). When I scroll to the last cell I check 3 properties: isTracking, isDragging and isDecelerating. When I am on the last cell drag a little bit to the left (to see pice of the previous cell) and then (without lifting the finger) drag to the right (anchor the cell). End touch and check properties.I have full-screen UICollectionView cells (firs