MBot Cube (DH kit): problems with B-stepper motor in RepG

I assembled the printer from the plywood DH kit. I don’t try to print anything. In ReplicatorG when I trying to control B-stepper motor printer performs X-axis offset instead and always to the right direction (X+). With A-stepper motor everything works correctly. At the same time, the movement of all axes is operating correctly. Why is this happening?