Unnexpected results using to_number()

Is this supposed to happen? I discovered this when I was experimenting with
converting a string to a number.

# SELECT to_number('12,454.8-', '99G999D9S');
to_number
-----------
-12454.8
(1 row)

# SELECT to_number('12,454.8-', '');
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!#

I am running PostgreSQL 7.0.2 on FreeBSD 3.4-STABLE (x86). Thanks,

- Andrew.