MX-100 1:many NAT not working as expected

1:many NAT on MX-100 not usable for zoom connector or barracuda spam firewall

I have discovered that the 1:many meraki NAT implementation will always send outgoing traffic on the primary public IP instead of the IP assigned to the 1:many NAT rule.
 
I have spend hours on trying to find out why I am not able to use these two NAT services:
 

1. zoom meeting connector which should  be  possible to configured using 1:many NAT unfortunately not on meraki MX-100 device:
   https://support.zoom.us/hc/en-us/articles/204898919-Configure-Meeting-Connector-Controller-Port-Forwarding
   The solution to this is not to use 1:many NAT rule and use 1:1 NAT unfortunately this will require two public IPs or more if you add other zoom on-premise services.
    
2. barracuda spam firewall and exchange server.
   I decided to offload some traffic from the barracuda firewall for traffic which is not related to SPAM checking and use the build in 1:many NAT instead of 1:1 on the MX-100.
   This resulted in outbound email be send using the primary IP instead of the assigned 1:many NAT
   This will result in SPF verification to fail and outgoing email be rejected from outside servers.
   Had to revert back to 1:1 NAT and deal with occasional overload on barracuda firewall due to web traffic.
    
   cheers