information_schema.referential_constraints broken?

This query:

select * from information_schema.referential_constraints;

under PG 8.4.5 (Windows platform) produces this error message:

ERROR: operator is not unique: smallint[] <@ smallint[]
LINE 1: select $1 <@ $2 and $2 <@ $1
^
HINT: Could not choose a best candidate operator. You might need to add explicit type casts.
QUERY: select $1 <@ $2 and $2 <@ $1
CONTEXT: SQL function "_pg_keysequal" during inlining

********** Error **********

ERROR: operator is not unique: smallint[] <@ smallint[]
SQL state: 42725
Hint: Could not choose a best candidate operator. You might need to add explicit type casts.
Context: SQL function "_pg_keysequal" during inlining

I don't have more recent 8.4 releases to try it on.
It works fine on PG 9.1.3.

Did anyone else experienced this problem?

Regards,
Igor Neyman