Can't figure out column type dependencies

Hi,

I'm looking to find all records in pg_depend that show that some columns
in my db depend on the 'timestamp' type. So I do this:

select * from pg_depend where refclassid=1247 and refobjid=1114;

1257 is the oid of the pg_type table and 1114 is the oid of the
timestamp type.

It returns just this:

australia=# select * from pg_depend where refclassid=1247 and refobjid=1114;
classid | objid | objsubid | refclassid | refobjid | refobjsubid | deptype
---------+-------+----------+------------+----------+-------------+---------
0 | 0 | 0 | 1247 | 1114 | 0 | p
(1 row)

How is that possible? I have heaps of columns that use the timestamp type:

select count(*) from pg_attribute where atttypid=1114;

If such dependencies aren't recorded, does the bit of code in alter
column type that deletes them ever do anything?

Chris