Timestamp precission question

Hello all,

I have one question about converting timestamps to text. I believed
that using to_char function with proper mask and casting by style
COLUMN::text is equal, but when I issue following query against  8.3.3
database it returns me different values (they differ on last position
of microsecconds value, maybe rounding error ?).
Could please somebody tell me what is the
reason ? I have tried to find some info about it on web but without
success.

Thanks in advance
Vaclav TVRDIK

WoC=> SELECT to_char(create_dat, 'YYYY-DD-MM HH24:MI:SS:US'),
create_dat::text
WoC-> from config
WoC-> where parameter_name = 'app_server_db_conn_pooler_connections';
          to_char           |         create_dat
----------------------------+----------------------------
 2008-02-09 12:12:15:214268 | 2008-09-02 12:12:15.214269
(1 row)