Strange error related to temporary tables

Postgres version: 8.1.3

I have a code similar to this pseudo-code:

try {
create temp table temp_report ...;
... do some processing using this table...
drop table temp_report;
commit;
} catch all errors {
rollback;
}

This code occasionally triggered the following error (couldn't reliably
reproduce):

SQL state: 42710

ERROR: type "temp_report" already exists

The code is possible to be executed in parallel by multiple threads, on
different connections, or in sequence on the same connection. I would
expect it in both cases to work correctly... in manual tests I was able
to create in parallel temporary tables named identically in different
connections, and on the same connection after rolling back the
transaction which created the first table... so I don't know what to try
to trigger this.

Any ideas what's the problem ?

TIA,
Csaba.