These limitations apply to standard and measure hierarchies:
You cannot add a data source column or metadata element into a hierarchy chain if the column or element already exists in the chain.
Use care when dragging and dropping multiple data source columns or metadata elements into a hierarchy chain. If one or more columns or elements are already present in the chain, the drop is rejected. When dragging multiple columns or elements into a hierarchy chain, be sure to select columns or elements that are not already present in the chain.