This is working for me.
Note that I implemented a new feature in 2.42.9h requested by several forum members. The cost multiplier is now manually changable whether one is using dynamic costs or not. You can see it on the Costs dialog.
If you are using dynamic costs, manually changing the cost multipler changes it that cycle and the dynaimc costs code modifies it from that new value going forward depending upon the hetertrof population relative to the thresholds as always.
If you are not using dynamic costs, manually setting the cost multipler simply multiplies all the other costs by that value each cycle.
If the cost multipler is zero (which it will be if the last sim you ran before this new one was a zerobot sim with no costs) then all costs will be multiplied by 0. I suspect this is why your veggies are not losing nrg when the sun is down.
If you still think there is a bug here, let me know (and post a sim!).
