Oracle BI - using Oracle ODBC driver

It seems that name of the connection pool has to be the same as the tnsnames entry if you are using the Oracle ODBC driver with Oracle BI. If it is different then all appears to be OK when using the administration tool but all falls apart when you try and run a report with cannot find entry in tnsnames. Put an entry in the relevant tnsnames.ora file which the same as the connection pool name and it all magically starts working. Good eh?