GROUP_BY with user functions

[Robert Enyedi]

Does Derby support user functions in GROUP BY clauses?
I'm thinking of the following scenario:

SELECT USER_FUNCTION(t1.column1)
FROM TABLE t1
GROUP BY USER_FUNCTION(t1.column1);

When I tried this with the latest 10.2.1.3 beta version, this is the 
error I get:

ERROR 42Y30: The SELECT list of a grouped query contains at least one 
invalid expression. If a SELECT list has a GROUP BY, the list may only 
contain valid grouping expressions and valid aggregate expressions.

Any ideas?

Thanks,
Robert