Strange results from to_timestamp

mydb=# select to_timestamp('00000000 0300','yyyymmdd hh24mi');
to_timestamp
---------------------------
0001-01-01 03:00:00+01 BC
(1 row)

Questionable, but probably valid.

mydb=# select to_timestamp(' 0300','yyyymmdd hh24mi');
to_timestamp
------------------------
0300-12-25 03:00:00+01
(1 row)

This puzzles me. Where is the 25th of december coming from?

mydb=# select to_timestamp(' 030004','yyyymmdd hh24mi');
to_timestamp
------------------------
0382-04-23 03:00:00+01
(1 row)

Same as above.

mydb=# select to_timestamp(' 040004','yyyymmdd hh24mi');
to_timestamp
------------------------
0509-10-10 04:00:00+01

I think all except the first one should raise a warning, isn't it? Where can I
find the source code of this function?

Best regards,
Mario Weilguni