Over Amperage when I change direction

Hi,

I use FBL2360 in RC to run a Maxon EC 90 flat motor in trapezoidal mode. When i go forward, everything goes right, fine response and nominal amperage(6A). However when It comes to go backwards, the motor works wrong. Either it works slower with growing amperage that make the motor heat (over 20A), either it doesn't move while the amperage are reaching a high value (around 10A) and then goes full speed with the same problem.
How can I solve that problem ?

Thanks for your help