Problem in fetching data from sys.dm_fts_index_keywords_by_document table for the first time

Hello,
Am storing a word's contents with full text index into a table in SQL SERVER 2008. The keyword is then retrieved using the code
SELECT display_term FROM sys.dm_fts_index_keywords_by_document ( DB_ID(), tableid) Where mycondition
Am executing a stored procedure from my application which saves the word document details into a table and again invokes a stored procedure right after the above save( containing the above code) inorder to retrieve the keyword. I find that during the first time when a fetch occurs from  sys.dm_fts_index_keywords_by_document, the keyword is not retrieved from the table though the data is present. When i execute the same for the second time, data is retrieved. I am not able to figure out the reason. I confirmed that in both the cases i have given same condition to retrieve a particular keyword. Is there any performance specific issues related to sys.dm_fts_index_keywords_by_documen ...