SBS 2008 Send As Permissions not staying

Hello

I have a SBS 2008 server that only keeps the Send as permissions for a couple of hours then just disappear. I can add Self or the users name via Exchange 2007 console or AD with the same results. The issues to only be with new accounts as the default when creating new user accounts is for Self to be added. I can add Full Permissions and it stays.

I look after a number of SBS 2008 and 2011 servers and ive only got this issue on 1 server.

Any Ideas would be help full.

Cheers