Unable to convert date to tm

Hello,

I get an error if I try to convert a date before 1970 into a timestamp:

# SELECT (date '1970-01-01')::timestamp;
timestamptz
------------------------
1970-01-01 00:00:00+01
(1 row)

# SELECT (date '1969-12-31')::timestamp;
ERROR: Unable to convert date to tm

I get this error using the RPM postgresql-7.2.1-5 (Red Hat) and
postgresql-7.2.2-1PGDG.
(Btw: What does "tm" stand for?)

On another Linux machine (which should be configured quite similar)
using RPM postgresql-7.2.1-2PGDG there is no error - both SELECT
statements work as expected.

Thx in advance,
Joerg Ludwig