Parent-child dimensions, historical values (SCD) and keys

Usually working with historical values in an SSAS cube is not really complicated. Think of a customer whose ZIP code changed over time which is modeled as a slowly changing dimension of type 2:

ID	Customer	ZIP	Current
1	John Doe	10000	false
2	John Doe	10200	false
3	John Doe	13041	true

If we don't include the ZIP-code in the MDX query, we just see the sales. For example, let's take a look at the following query: