Workers leave resources on roof

Workers leave wood on roof.
It appears that the workers put down their wood on the roof to go eat but when they return they dont always pick up the wood they put down on the roof. The roof is then completed and the scaffolding removed, leaving the wood on the roof.

Does the wood get left on the roof stll if you build a ladder after the scaffolding is dismantled? Possibly a pathfinding/recognition bug.

OK it looks like if I build a ladder to the roof after the fact, the workers will retrieve the wood.