Full text t_tsquery is giving error - Mailing list pgsql-general

I am getting the following results:

select * from ts_debug('Rumman (AI)');

   alias   |   description   | token  |    dictionaries    |  dictionary  | lexemes 
-----------+-----------------+--------+--------------------+--------------+----------
 asciiword | Word, all ASCII | Rumman | {syn,english_stem} | english_stem | {rumman}
 blank     | Space symbols   |  (     | {}                 |              |
 asciiword | Word, all ASCII | AI     | {syn,english_stem} | english_stem | {ai}
 blank     | Space symbols   | )      | {}                 |              |
(4 rows)

But,

select to_tsquery('Rumman (AI)');

ERROR:  syntax error in tsquery: "Rumman (AI)"

I don't know why this is happening.
Any idea please.