Networks settings and mac address

If i edit my default connection ie "auto eth0" add ipaddress and save it as superuser it goes fine
but when i add custom mac id given by my isp it dosent work ie the connection is listed in network manager but not in my connect or disconnected connections ie " when we click on that network icon and connect whichever connection we want there "auto eth0 "isnt listed instead new connection gets created ie "auto ethernet"

to tell by steps :
1.made a clean install of ubuntu 10.04and ubuntu 9.10
2.edited default connection ie "auto eth0" added my ipaddress and dns servers.
3.if i save now everything will be saved and my connection will be listed both in network manager and also in quick connect ie when we click on network icon @ we select which connection we want to connect ...
(but internet will not work as isp now has given me custom mac address for my use and i will have to use it)
4.but now if i add a new mac address in mac address tab of connection "auto eth0" and save it the connection will be listed in network manager under "wired " tab but it will not be seen when i click on network icon for connectiong "auto eth0" instead a new connection gets created called "auto ethernet" and if i add mac address to it even that connection will not be shown and new connection will be created .. :(
without mac address i cannot use internet on ubuntu
found this problem in 4-5 distros till now .......