How can you have an Exclusive Lock on nothing? please help me understand this lock monitoring query output

Hi. I use the following query (from
http://wiki.postgresql.org/wiki/Lock_Monitoring)
to monitor locks; and I've got an ExlusiveLock that does not have a relation
name associated with it. What is locked with the Exclusive Lock in this case,
please? (it's between "d" and "e" tables below)

psql -U postgres -d ddcKeyGen -c 'select
pg_class.relname,pg_locks.transactionid, pg_locks.mode, pg_locks.granted,
pg_stat_activity.usename,substr(pg_stat_activity.current_query,1,50),
pg_stat_activity.query_start,
age(now(),pg_stat_activity.query_start) as "age", pg_stat_activity.procpid
from pg_stat_activity,pg_locks left
outer join pg_class on (pg_locks.relation = pg_class.oid)
where pg_locks.pid=pg_stat_activity.procpid order by query_start;'

Output:

a_index | | AccessShareLock
| t | user |
| 2011-04-14 17:36:01.257669-07 | 00:21:28.847825 | 16798
b_index | | AccessShareLock
| t | user |
| 2011-04-14 17:36:01.257669-07 | 00:21:28.847825 | 16798
c_index | | AccessShareLock
| t | user |
| 2011-04-14 17:36:01.257669-07 | 00:21:28.847825 | 16798
d | |
AccessShareLock | t | user |
| 2011-04-14 17:36:01.257669-07 |
00:21:28.847825 | 16798
|
| ExclusiveLock | t | user |
| 2011-04-14 17:36:01.257669-07 |
00:21:28.847825 | 16798
e | |
AccessShareLock | t | user |
| 2011-04-14 17:36:01.257669-07 |
00:21:28.847825 | 16798
f_index | | ShareLock
| t | user |
| 2011-04-14 17:36:01.257669-07 | 00:21:28.847825 | 16798
g_index | | AccessShareLock | t
| user | |
2011-04-14 17:36:01.257669-07 | 00:21:28.847825 | 16798

Thanks,
Aleksey