What you are seeing is the correct behavior which resulted from you selecting "unrestricted with full admin" level of rights for the
agent signer.
The full admin allows you to by-pass ACL and reader fields. I suspect the level you really wanted to use is "unrestricted", which gives
you everything but the ability to by-pass ACL and reader fields.
Here are some useful links for full admin explanation:
http://www-12.lotus.com/ldd/doc/domino_notes/Rnext/help6_admin.nsf/0/ae18e6833afcfbf285256c1d003982b5?OpenDocument
http://www-10.lotus.com/ldd/today.nsf/62f62847467a8f78052568a80055b380/177bbe55c6848ae000256c44003aee17?OpenDocument&Highlight=0,kadashevich