Another orderby problem

Just joined the list and have seen in the archive the thread on orderby.  But 
mine seems different.

I have a finanancial application with account and transactions which go 
between accounts (source and destination) but in which one either can be 
null.

I am attempting to read an account and sort all the transactions by date.

Here are the transactions

id |    date    |  src  |  dst  |        description        | amount
----+------------+-------+-------+---------------------------+--------11 | 2005-06-05 |       | Sarah | Sarah Petrol
         |  27.7412 | 0005-06-05 | Sarah |       | Ben 21st Birthday Pressie |    -4113 | 0005-06-05 |       | Sarah |
Cashfrom Mum             |     6014 | 0005-06-08 |       | Sarah | Petrol                    |  27.3315 | 0005-06-10 |
    | Sarah | Petrol Allowance          |    -40
 

This is the SQL

select name, id, transaction.date as tdate, description, -amount as amount
from account left join transaction on name=src where name = 'Sarah' 
union
select name, id, transaction.date as tdate, description, amount
from account join transaction on name=dst where name ='Sarah'
order by tdate asc;
name  | id |   tdate    |        description        | amount
-------+----+------------+---------------------------+--------Sarah | 12 | 0005-06-05 | Ben 21st Birthday Pressie |
41Sarah| 13 | 0005-06-05 | Cash from Mum             |     60Sarah | 14 | 0005-06-08 | Petrol                    |
27.33Sarah| 15 | 0005-06-10 | Petrol Allowance          |    -40Sarah | 11 | 2005-06-05 | Sarah Petrol              |
27.74
(5 rows)

I can't figure out why the dates are not in order (see transaction 11 is out 
of place).  

for reference the transaction table has the "date" field of type "date"



-- 
Alan Chandler
http://www.chandlerfamily.org.uk
Open Source. It's the difference between trust and antitrust.