In the Document, it's stated that:

"The use of absorption costing can lead to omission of segment costs because nonmanufacturing costs are not included as costs of a product." as well as "Using absorption costing for segmented income statements can lead to: under-costing of segments & omission of upstream and downstream costs."

How does this happen though? I don't understand how absorption costing can lead to these problems. I'm hoping a tutor can expand on this and explain it in simpler terms.