recently I discovered one issue in the SQL Server Integration Services (SSIS), which I would name "bug". I decided to inform everyone about this thing - perhaps, this will help you.
So, imagine the following situation: you have a DB-table with a column named "BK" (for instance). You wish to export this table into CSV-file. You configure the output of "ASCII Destination" in such a way, that "BK" column is redirected to "BK_QUE" column of the ASCII file (and "BK" column of the file should be left empty). What does SSIS do? It outputs "BK" into "BK_QUE" (as desired) AND - at the same time - into "BK"! See the screen-shot for more details.
So, always keep in mind, that SSIS links the columns with the equal names by default (even if you set "Ignore" explicitly), if you create such an export item in your Data Flow Task.