Map-valued collections in HQL queries

[Alex Gr�nholm]

SELECT INDICES(pi.amounts) AS cat, pi.supplierName, SUM(ELEMENTS(pi.amounts)) FROM PurchaseInvoice pi WHERE pi.dueDate >= :startDate AND pi.dueDate <= :endDate GROUP BY cat, pi.supplierName

The above HQL query does not work, because Hibernate fails to connect the "cat" alias in the GROUP BY clause to the one being selected.
According to the Hibernate manual, it should be possible to give a function result an alias. However, Hibernate does not translate it to its proper value in the native SQL query.
What am I doing wrong?

The PurchaseInvoice class has:

@CollectionOfElements
public Map<String, Double> getAmounts() {
    return amounts;
}