Index in its own tablespace-PostgreSQL9.2 AS

I have two tablespaces tb1 and tb2. tb1 and tb2 have their own file systems.tb1 is for a huge table with 2 billion rows .tb2 is for rest of the tables.So , I have my huge table created in tb1 and now when I am trying to create an index on this table the index is being created in tb2 even though I explicitly mentioned to create the index in tb1 in CREATE INDEX statement.Eventually , the index creation is failing due to less disk space in tb2.
I also do not see any kind of information in pg_log.

OS: Redhat Linux
PostgreSQLVersion : 9.2 AS

Please help!!