I usually fill my excavator bucket from a dump truck, then use the terrafarm setting that increases ground level and dump it into the trench to raise the ground level. Then I use the excavator bucket to level the ground at the top of the trench
So, after playing around I think it's your version of terrafarm and why it's not working. The only reason I say that is there is no raise function and only a lower option unless i'm missing it somewhere
I use my version of Terrafarm and it works perfect for me. are you sure you are checking the discharge options? lowering isnt even an option for the discharge, that is only an option for the digging option if I remember correctly..