security in accounting flexfield segment - posting

Dear experts,
I am using an old version of oracle application 11.5.0,

I set up security rules for an accounting flexfield segment which is ok for query/enter journal line, but not for the posting of journal.

I still can post journals which I have not the right to see the lines, 

I have another problem, even I can not see the journal lines of another user journal , I still can add lines (my flexfield combination)  in his journal.

can I do something to resolve this problems ??

thank you advance

Denisa