maintenance_work_mem + create index

Hi,

I see my application creating temporary files while creating an index.
LOG:  temporary file: path "base/pgsql_tmp/pgsql_tmp7076.0", size 779853824
STATEMENT:  CREATE INDEX IDX_LPA_LINKID ON NNDB.LPA (LINK_ID);

So I checked this again and raised afterwards maintenance_work_mem step by step up 64GB.
I logged in via psql, run the following statements
set maintenance_work_mem = '64GB';
CREATE INDEX IDX_LPA_LINKID ON NNDB.LPA (LINK_ID);

But still I get that evil message in the log file about creating a temporary file.
I also raised work_mem in my session up to 32GB - again without changing the behavior.

According to the postgres docs http://www.postgresql.org/docs/8.4/static/populate.html#POPULATE-WORK-MEM this is supposed to help.
Any ideas?

I'm running postgres 8.4 64 bit on Linux from an enterprisedb package.
# file /var/lib/pgsql/bin/postgres
/var/lib/pgsql/bin/postgres: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), for GNU/Linux 2.4.0, dynamically linked (uses shared libs), not stripped


Best Regards,
Uwe