Mangle breaks voip - SIP registration

Im using the gigaset handsets and connecting via SIP function.

This is my config, very basic:

   ip firewall address-list print detail
4   list=Allowed Internet address=192.168.5.0/24



 ip firewall nat print detail 
Flags: X - disabled, I - invalid, D - dynamic 

 1   chain=srcnat action=masquerade src-address-list=Allowed Internet 
     out-interface=2 ADSL2 

 3   chain=srcnat action=masquerade src-address-list=Allowed Internet 
     out-interface=4 ADSL4



ip route:
 3 A S  ;;; Group2
        dst-address=0.0.0.0/0 gateway=2 ADSL2 
        gateway-status=2 ADSL2 reachable check-gateway=ping distance=1 
        scope=30 target-scope=10 routing-mark=Group2 

 4 A S  ;;; Default Route
        dst-address=0.0.0.0/0 gateway=4 ADSL4 
        gateway-status=4 ADSL4 reachable distance=1 scope=30 target-scope=10

everything working fine. BUT when i add this rule:

 4 X ;;; Siemans thru Group2
     chain=prerouting action=mark-routing new-routing-mark=Group3 
     passthrough=no src-address=192.168.5.1

Then: SIP registration fails and cant use voip, basically, no connection.
i want to route the siemans gigaset handset (my sip device) to ADSL2
how would i do that without breaking the connection?

Hi
are you use UDP Protocol for sip registration or TCP?

im not really sure buddy, how would i check that? here is a screenshot of my settings on the sip device
sip settings.PNG