Is there a limit on CATSEARCH using CONTEXT grammar?

On Oracle 10.2.
 If I create a CATSEARCH index on a field, then use CONTEXT grammar to search for a word with wildcards, there appears to be a limit of 60 characters, after which it doesn't return a result.

e.g.

The following works because the search string is 60 long:
SELECT DESCRIPTION
FROM   test
WHERE  CATSEARCH (DESCRIPTION,
'<query>
      <textquery grammar="context">
%insertintaaadocumenttypevarDOCUMENTTYPEKEYDOCUMENTTYPECODEVA%
      </textquery>
 </query>',null) > 0;

whereas the following returns nothing because the search string is 61 long:
SELECT DESCRIPTION
FROM   test
WHERE  CATSEARCH (DESCRIPTION,
'<query>
      <textquery grammar="context">
%insertintaaadocumenttypevarDOCUMENTTYPEKEYDOCUMENTTYPECODEVAL%
      </textquery>
 </query>',null) > 0;

Is this documented behaviour, and if so, can someone point me to the document. Alternatively, is there a workaround?