Queries which involve a mix of partially applicable dimensions can give wrong results. E.g.
with member [Measures].[allW] as
'([Measures].[Unit Sales], [Warehouse].[All Warehouses])'
select NON EMPTY Crossjoin(
[Warehouse].[State Province].Members, [Product].[All Products].children)
from [Warehouse and Sales];
returns an empty set, even though it should return a list of warehouses / products.
Attaching a write-up with more detail.