Does Comcast Bind Static IP to MAC address?

Hello,

We recently signed up for Comcast business class, and opted for a static IP. We turned the modem into passthrough mode with supports help. I have a nice router running RouterOS, very configurable. Problem is, this thing cannot get out to the web. 

I can ping the static IP from the WAN port, I can ping the gateway IP, but I cannot ping 8.8.8.8.

If I hook up only my laptop to the modem on its WAN/LAN port, manually configure ipv4 to be the static IP, correct gateway, subnet, DNS, I can get out and ping 8.8.8.8. 

I wonder tho, if the modem is doing some sort of simple NAT masq when my laptop's connected as the static, where Comcast still sees the modems MAC. But when I have my router connected in the same way, my router presents its MAC and we get blocked? 

So my simple question is, does Comcast associate, whitelist, or otherwise bind the MAC of the modem to the static IP address? 

Knowing this will really help me in my troubleshooting efforts here.

Thanks!