Ordering problem with varchar (DESC)

Hi all,

We have a column (varchar) that has plain text time and it is indexed.
When I do a query with the index, all the data is in the right order,
but when I user ORDER BY .. DESC, the order is messed up. Example:

By index 1: (date, time, data)
SELECT * from t1;
date (date type) time (varchar) data
2007-01-17 8h40 d1
2007-01-30 9h30 d2
2007-01-30 12h00 d3
2007-01-30 13h45 d4
2007-01-30 17h20 d5

SELECT * from t1 ORDER BY date, time DESC;
date (date type) time (varchar) data
2007-01-30 9h30 d2
2007-01-30 17h20 d5
2007-01-30 13h45 d4
2007-01-30 12h00 d3
2007-01-17 8h40 d1

I don't know why, this is like if the 'time' varchar was trimmed then
used for the ordering.

How can I fix that so that the result is exactly like the first one but
perfectly reversed in it's order?

Best regards.

--
Alexandre Leclerc