pg_freespacemap question

Hi,

I tried pg_freespacemap and found strange result:

test=# select * from pg_freespacemap where blockfreebytes = 0;blockid | relfilenode | reltablespace | reldatabase |
relblocknumber| blockfreebytes 
 
---------+-------------+---------------+-------------+----------------+----------------     25 |        2619 |
1663|       16403 |              0 |              0     63 |        2619 |          1663 |       16384 |             10
|             0
 
(2 rows)

Is it possible that a free space map entry has 0 blockfreebytes?
--
Tatsuo Ishii
SRA OSS, Inc. Japan