domain on bit(N) type produces strange results

Creating a domain on bit(N) doesn't seem to work as expected when casting
to the domain type.

CREATE DOMAIN bit4 AS bit(4);

SELECT 7::bit(4), 7::bit4;
 bit  | bit4
------+------
 0111 | 1000
(1 row)


Reported in #postgresql by msw_alt.

Kris Jurka