Problem with dropping a tablespace

Hello,

I'm unable to drop a recently created tablespace (the partition on which the
tablespace relies on, run out of space - postgresql seems to have a problem,
now):

template1=# drop tablespace disk1;
ERROR: tablespace "disk1" is not empty

Huh? Okay...lets dig into...

template1=# select oid from pg_tablespace where spcname = 'disk1';
oid
-----------
594611987
(1 row)

template1=# select * from pg_tablespace_databases(594611987);
pg_tablespace_databases
-------------------------
595675173
(1 row)

Aha...so there seems to be a database associated to this tablespace - lets see
which one -

template1=# select * from pg_database where oid = 595675173;
datname | datdba | encoding | datistemplate | datallowconn | datlastsysoid |
datvacuumxid | datfrozenxid | dattablespace | datconfig | datacl
---------+--------+----------+---------------+--------------+---------------+--------------+--------------+---------------+-----------+--------
(0 rows)

Mhh. Nothing.

How may I delete the tablespace manually?

Best regards

Oliver