equal and like

Hi List,

This is my first post to this list.
Our database moved to a larger partition.
And now I have a problem with a select query:
db=# SELECT id, login FROM u WHERE login LIKE 'bellamarth';
   id   |    login
--------+-------------
 173002 | bellamarth
(1 row)

db=# SELECT id, login FROM u WHERE login = 'bellamarth';
 id | login
----+-------
(0 rows)

The type of login is text.
What is the problem with the equal sign?
psql server version: 8.2.11

Could you help me?

Gabor