Timestamp in PG - 7.1 & 7.2

Hi,
I've observed this:
Here is output from PostgreSQL 7.1.2:

trapdb=# select cast(datetime(1057637700) as timestamp);
?column?
---------------------------
2003-07-08 09:45:00+05:30
(1 row)

Here is output from PostgreSQL 7.2.4:

trapdb=# select cast(datetime(1057637700) as timestamp);
timestamp
---------------------------
2003-07-07 22:45:00+05:30
(1 row)

I've migrated from PG - 7.1.2 to 7.2.4.

My timezone is set as "IST" in both cases.
Is this any version problem or I'm missing any envirnonment setting?

Help is appreciated....

Thanks,
Anagha