Integration Services :: Cannot Get Current Row Value Of Column

I have successfully created a linked server between SQL Server 2008 R2 and a Postgres db, and all is working fine, except when I try to run a stored procedure that returns a TEXT column.The top lines of the stored procedure (function in postgres) that is called are:

CREATE OR REPLACE FUNCTION get_defects()
RETURNS TABLE(defectid bigint, featurevalues text) AS ...

The function obviously executes correctly in postgres, however when I try to execute the function in SQL Server via the linked server:

SELECT *
FROM OPENQUERY(POSTGRES, 'SELECT * FROM get_defects()')
I get the error:

OLE DB provider "MSDASQL" for linked server "POSTGRES" returned message "Requested conversion is not supported.".
Msg 7341, Level 16, State 2, Line 1

Cannot get the current row value of column "[MSDASQL].featurevalues" from OLE DB provider "MSDASQL" for linked server "POSTGRES".The problem seems to be when trying to return the TEXT column featurevalues, as the following query executes as expected:

SELECT defectid
FROM OPENQUERY(POSTGRES, 'SELECT * FROM get_defects()')