Ok just did a TCP dump from the ER8 on eth0 with eth1 enabled, then disabled...
Traffic still comes in on port 8080 from the sites IP. Which leads me to suspect the traffice flowing out is the problem when enabling eth1.
Eth1 is failover only and weighted at 0 however they have the same route distance. I'm reluctant to add a static route as I assume that would break the ability for dynamic routing should an actual failure occure on eth0.
Don't know what to do from here...