Oh, my mistake, I missed your post, but it is exactly the same problem, so the implementation is obviously not correct. Also I think, that behavior of Trade mode in case of negative prices is not correct for that reason, because if price became negative, the goal should be cover consumption and also charge the battery from grid, not from PV (I can imagine this in Green mode, but not in Trade mode).
I am using DESS in Trade mode, because I want to feed-in PV energy directly to grid in case of higher positive price (especially in the morning) and after that when price drops use PV to charge the batteries. Second benefit should be to use as much energy from grid as possible in case of negative price to get better final energy bill (obviously :–) ), to help stabilize the grid (when there is a lot of excess energy) and to not use PV (extend the life of solar panels and MPPTs).