Average vs Average_Pop

Has anyone ever notice strange behavior in RPAS when using average vs. average_pop aggregation methods.  Consider the following scenario:

If you have a measure that uses average/prop, it aggs and spreads as follows:

		Enter 12 at Department
Department	6	12
Class 1
Class 2	5	10
Class 3	6	12
Class 4	9	18
Class 5	10	20

However if you have a measure that uses average_pop/prop, it spreads as follows:

		Enter 12 at Department
Department	7.5	2.4
Class 1
Class 2	5	2
Class 3	6	2
Class 4	9	3
Class 5	10	3

The first scenario seems wrong as I would expect both to behave as specified in the second case (spreads 12 proportionally down to each class and recalculates the department level (based on average).  But I'm curious as why they behave differently.