my horse does the same, just have to be gentler with the hands and use leg half halt and seat more, doesn't cure it completely but also slowing the trot down before halting so he is more prepared and counting down the strides until you halt. Sometimes exageratting the moves ie half halting more, sitting deeper helps and doing it less and less everytime until the move becomes really subtle and he will know what it means. Practise a lot will help, doing it a few times in one circle, so he knows what he is supposed to be doing. its good because it gets him listening and responsive. hope this helps
