I don't know, if this is an inconsistence or a bug, but here a possible workaround:
select current_timestamp::abstime::int4 as score, current_timestamp::abstime::int4 + 1 as "score + 1" order by "score + 1";
LudwigThis works:
critik=# select current_timestamp::abstime::int4 as score order by score;
This doesn't:
critik=# select current_timestamp::abstime::int4 as score order by score + 1;
ERROR: column "score" does not exist
LINE 1: ...urrent_timestamp::abstime::int4 as score order by score + 1 ...