We have a similar problem where I can't route traffic from the LAN to the Wireless network and back.
All our Mac's wired through various thunderbolt, USB and internally connected NIC and use a common WiFi network. No matter which machine we try, including an air port, sharing the connection does not allow bridging between the two networks. I think it might be because the WiFi is secured with WPA2 and therefore the unsecured LAN is prevented from connecting (as it would effectively allow any computer on the LAN to access the WiFi). Has anyone else come across this or is it just my imagination?
Also, our printers and Mini are all on the LAN and we can't connect to them unless the LAN is at the top of the Service list in Network preferences. However, the Internet access is through the WiFi connection and does not work unless the WiFi is at the top of the Service list. If I unplug the Ethernet then the WiFi works fine and if I turn off the WiFi the LAN works fine - but not both at the same time! Any suggestions on how to make them both work at the same time - Route? DNS?