varchar of length > 32

We are using a table with a primary key of type varchar[50].
If we try to find entries with select * from <table> where <table.key> =
'<text>';
entries with a key length of more than 32 characters are not found.
Entries with a shorter key are found. Using "Like" instead of "=" works for
varchar keys with length > 32 as well.

Does anybody know about this Problem ?
(We use PostgresQL 7.4.1)

Thanks in advance,
Christian Enklaar.