last_vacuum field is not updating

Why does vacuum table is not updating the field last_vacuum of
pg_stat_user_tables?

select * from pg_stat_user_tables where relname = 'table1';
-[ RECORD 1 ]-----+------------------------------
relid | 5452445
schemaname | public
relname | table1
seq_scan | 54911
seq_tup_read | 373562142
idx_scan | 2773802
idx_tup_fetch | 125909227
n_tup_ins | 889595
n_tup_upd | 530602
n_tup_del | 529037
n_tup_hot_upd | 162199
n_live_tup | 360526
n_dead_tup | 0
*last_vacuum | 2013-06-29 20:04:15.391413-04*
last_autovacuum | 2013-05-01 00:55:01.970799-04
last_analyze | 2013-07-15 10:55:40.870926-04
last_autoanalyze | 2013-05-01 06:04:12.905961-04
vacuum_count | 92
autovacuum_count | 248
analyze_count | 94
autoanalyze_count | 560

psql# *vacuum analyze verbose table1;*

INFO: vacuuming "public.table1"
INFO: index "table1_pkey" now contains 360965 row versions in 1878 pages
DETAIL: 0 index row versions were removed.
326 index pages have been deleted, 305 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: "table1": found 0 removable, 1116 nonremovable row versions in 30
out of 2286 pages
DETAIL: 0 dead row versions cannot be removed yet.
There were 6720 unused item pointers.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
VACUUM

select * from pg_stat_user_tables where relname = 'table1';
-[ RECORD 1 ]-----+------------------------------
relid | 5452445
schemaname | public
relname | table1
seq_scan | 54911
seq_tup_read | 373562142
idx_scan | 2773802
idx_tup_fetch | 125909227
n_tup_ins | 889595
n_tup_upd | 530602
n_tup_del | 529037
n_tup_hot_upd | 162199
n_live_tup | 360526
n_dead_tup | 0
*last_vacuum | 2013-06-29 20:04:15.391413-04*
last_autovacuum | 2013-05-01 00:55:01.970799-04
last_analyze | 2013-07-15 10:55:40.870926-04
last_autoanalyze | 2013-05-01 06:04:12.905961-04
vacuum_count | 92
autovacuum_count | 248
analyze_count | 94
autoanalyze_count | 560