The full fare Y prices should be the same no matter where you buy them... even other airlines would be able to sell them to you for that price.
Just as a side issue - how did you get on with LH in SIN for the CGK run - did the silly infoflyway spit the dummy about the turnaround at SIN? If you are having problems you could try this
http://www.airfares.com.sg/airfares/...lh_jakarta.htm (I am in no way connected with these people - and have never delt with them but I understand them to be fair to deal with)
Best Regards
Bradley