unsupported types in 8.0.1

I'm attempting to upgrade to 8.0.1, and have hit my latest hurdle: an
unsupported type when I try to compare ints. Example:

gr-test=> \d invitecodes
Table "public.invitecodes"
Column | Type | Modifiers
------------+---------
+-----------------------------------------------------------------
invite | integer | not null default
nextval('public.invitecodes_invite_seq'::text)
sponsor | bigint | not null
generated | integer | not null default ((now())::abstime)::integer
expires | integer | not null
acceptedby | bigint |
acceptedon | integer |
expiredon | integer |

gr-test=> select expires from invitecodes;
expires
------------
1111611373
1111551093
1112139900
1112169368
(4 rows)

gr-test=> select expires from invitecodes where expires <
((now())::abstime)::int4;
ERROR: unsupported type: 23

gr-test=> select expires from invitecodes where expires > 1;
expires
------------
1111611373
1111551093
1112139900
1112169368
(4 rows)

gr-test=> select expires from invitecodes where 1 <
((now())::abstime)::int4;
expires
------------
1111611373
1111551093
1112139900
1112169368
(4 rows)

I haven't a clue how to go about debugging this. Any pointers?