CONSTRAINT does not show when applying a EXCLUDE constraint -- and what about Enterprise Architect?

Dear list,

To rule out any double combination of two identifiers, in any order, I
applied the following constraint to a table:

CREATE TABLE test(
object_id INTEGER,
subject_id INTEGER,
CONSTRAINT "EXCL_double_combi" EXCLUDE USING btree (imm_LEAST(subject_id,
object_id) WITH =, imm_GREATEST(subject_id, object_id) WITH =)
);

The imm_xxxxx functions are IMMUTABLE wrappers around LEAST() and GREATEST()
respectively, in order to get the index to work...

pgsql Command "\d test" produces the following:
Table "public.test"
Column | Type | Modifiers
------------+---------+-----------
object_id | integer |
subject_id | integer |
Indexes:
"EXCL_double_combi" EXCLUDE USING btree (imm_least(subject_id,
object_id) WITH =, imm_greatest(subject_id, object_id) WITH =)

As I read it, an indexed in indeed being maintained, however it is not
regarded a CONSTRAINT... Yet, the set-up works as like a charm :)) This
online example shows a different summary:
http://www.depesz.com/index.php/2010/01/03/waiting-for-8-5-exclusion-constraints/
Would this be an earlier / older version of PostgreSQL? I'm running 9.0.2,
on Windows 7

By the way: has any one experience using EXCLUDE constraint inside
Enterprise Architect? Since this is a pretty new database feature, it seems
not yet supported by EA?

Looking forward to any of you sharing your experiences,
kind regards,

Rob