Copy db - lose login mapping

Whenever I copy my production db back to my development server i lose the
user mapping for my app account and have to drop the db user, then remap the
login to the correct db. Then I have to reassign permissions to the user.
How can I prevent this from happening?
ThanksHi
http://dimantdatabasesolutions.blogspot.com/2007/04/sql-or-windows-authentication.html
"ken s" <kens@.discussions.microsoft.com> wrote in message
news:4B16A51F-FAD3-4D86-8D5D-1C0A03DBD660@.microsoft.com...
> Whenever I copy my production db back to my development server i lose the
> user mapping for my app account and have to drop the db user, then remap
> the
> login to the correct db. Then I have to reassign permissions to the user.
> How can I prevent this from happening?
> Thanks
>sqlsql