problem with sendmail in sid

["Martin Maciaszek" <mmaciaszek@lydall.com>]

I'm trying to use gmx as my smarthost. For this to work I have to rewrite my sender address. I want to use a combination of masqurading + genericstable (I'm not quite sure if I really need masquerading for this).
Here is a short description of my set up:
my hostname: nexus.shadowrun.not
my login: fastjack
desired sender address: mmaciaszek@gmx.net 

I added the following lines to my sendmail.mc:
[...]
dnl masquerading options
GENERICS_DOMAIN(`nexus.shadowrun.not')dnl
MASQUERADE_AS(`gmx.net')dnl
FEATURE(`masquerade_entire_domain')dnl
FEATURE(`masquerade_envelope')dnl
dnl genericstable options
FEATURE(`genericstable',`hash -o /etc/mail/genericstable')dnl
[...]

my /etc/mail/genericstable contains the following line:
fastjack                        mmaciaszek@gmx.net 

When I start a queue run sendmail tries to deliver the mails to my smarthost with fastjack@gmx.net as the sender. What is wrong here? It used to work before.

Cheers
Martin