Something wacko about EXPLAIN cost stats

Current CVS sources are giving silly values for the cost fields of
EXPLAIN output:

treetest=> explain select * from marketorderhistory order by ordertime;
NOTICE:  QUERY PLAN:

Sort  (cost=??????? size=1610612736 width=1081364283) ->  Seq Scan on marketorderhistory  (cost=??????? size=1610612736
width=108136
4283)

EXPLAIN
treetest=> explain select * from marketorderhistory where ordertime = 'now';
NOTICE:  QUERY PLAN:

Index Scan using marketorderhistory_ordertime_in on marketorderhistory  (cost=??
????? size=-536870912 width=1074351372)

EXPLAIN

Looks the same before and after VACUUM, btw.
        regards, tom lane