PG7.4 ordering operator

Testing postgis support in PG7.4 (2003-11-11)
I've encountered to this problem:

ERROR: could not identify an ordering operator for type geometry
HINT: Use an explicit ordering operator or modify the query.

Whenever I issue one of these commands:

gis=# select the_geom from table1 UNION select the_geom from table2;
gis=# select DISTINCT the_geom from table1;
gis=# select the_geom from table1 ORDER BY the_geom;

Operators '<', '>', '=' are available:

oprname | leftoperand | rightoperand
---------+-------------+--------------
<< | geometry | geometry
&< | geometry | geometry
&& | geometry | geometry
&> | geometry | geometry
>> | geometry | geometry
~= | geometry | geometry
@ | geometry | geometry
~ | geometry | geometry
= | geometry | geometry
< | geometry | geometry
> | geometry | geometry
(11 rows)

Previous PG versions does not show this problem.
Any hint on what might be missing ?

--strk;