PostgreSQL 9.1beta 1 Some domains not being able to be auto cast to their base type

In regression testing PostGIS 2.0, our topology module regression tests are
failing in PostgreSQL 9.1 beta.

We have a PostGIS ticket open for it here, but we suspect it's a PostgreSQL
9.1 bug and would like to close it out.
http://trac.osgeo.org/postgis/ticket/980

Our domain type is defined as:

CREATE DOMAIN topoelementarray
AS integer[][]
CONSTRAINT dimensions CHECK ((((array_upper(VALUE, 2) IS NOT NULL) AND
(array_upper(VALUE, 2) = 2)) AND (array_upper(VALUE, 3) IS NULL)));

If I try this in PostgreSQL 9.1 beta1:

SELECT array_upper(ARRAY[ARRAY[1,2], ARRAY[3,4]]::topoelementarray,1);

I get error:
function array_upper(topoelementarray, integer) does not exist

In my PostgreSQL 9.0 and 8.4 the above operation works fine.

Thanks,
Regina