Motor speed is not the same in both direction

Hi I am testing My DC motors using mchelper. I am facing a weird behavior, I have a DC motor connected to outputs 4 & 5, If I set the speed to 1023 and direction to 1 the motor operates normally; however If I change the direction leaving the same value for speed, the motor makes much less rpms, please note that I do not notice this behavior if I connect the motor to other outputs. is it possible that there is something wrong in the outputs. Best Regards, mrizk