PostgreSQL 9.2.4 temp files never released?

I've a 12Gb database running without problems in Linux Centos 64bit for
years now.
Looking database statistics (in pgAdmin III), I can see that there are
366 temporary files, and they sum up 11,863,839,867 bytes in size.

Is that normal? When will this space be released?

I've restarted the server, but seems those files (in number and in size)
are just growing and growing...

Regards,

Edson Richter