At present the Apex Calendar does override the column sort added to the SQL statement by the Date column used.
There is a trick to override this functionality, you need to modify your SQL statement to achieve the same.
select display_column, cast(date_column as timestamp) + numtodsinterval('0.00' || rownum,'SECOND') date_column, sort_column
from
(select display_column, date_column, sort_column
from your_table
order by sort_column desc)
In the above example the Calendar data will be sorted on sort_column in a descending order.
