I found that this occurs when work on a structure has it’s workers enter into mealtime suspended working. When a worker drops an item in this manner it is outside the resource table for the town and is considered unclaimed resources. When building, workers gather available resources in the stockpile before tasking to find nearby unclaimed resources.
This can be avoided by tagging in the suspended AI model when it enters into the mealtime mode. A tag is created and attached to the end of the eating segment and then is used to return to the last know location of the work and resume working. Or a method to employ better resource allocation, such as an immediate mode for workers that only begins after returning to their last working position before returning to work mode. EG the end of the eating mode is not until it returns full circle to the last end of the work shift.
Sorry if this is a bit confusing, AI and heap management is a bit of a spaghetti factory from time to time.