Lumber starts disappearing after dropping/stacking it on a single tile past 100 tons. It does not start showing more stacks of lumber (compared to having multiple tons of regolith).
The environment was in a vacuum, the lumber dropped by a conveyor chute and swept by sweepers to be delivered to the ethanol distillers.
As the dupes delivered to the conveyor loader to have it dropped from the chute, whenever the stack got "past" 100 tons, if the sweeper picked up from the stack, the amount of lumber would start to decrease from 100 tons, not as if there was more than 100 tons or that there were multiple stacks.
Have item stacked/dropped on a single tile "past" 100 tons, then immediately have items used for other purposes