GS108EV2 802.1q vs port based VLAN

Can someone help me to understand what's going on 🙂

My apartment has a somewhat strange IPTV multicast delivery where both internet and IPTV (even though in two different IP surbents) are delivered in the same Ethernet socket (without 802.1q tags; I double checked using wireshark).

If I use the configuration as seen in picture all devices work as expected. I have two VLANS (all ports untagged) configured in GS108EV2 which handles local-subnet, WAN and IPTV subnets. Under this config the Router gets the correct WAN IP and the IPTV box also gets the correct IP (in a different subnet compared to WAN). 

My questions are:

1. How the IPTV box gets a IP in a different subnet compared to WAN? If I use wireshark by mirroring port-1 I can see both router and IPTV uses DHCP? 
2. More intersting question is why I cannot replace above configuration with a basic port based VLAN? I tried it (VLAN1: ports 1,2,8 and VLAN2: ports 3-7). But then Nvidia Shield which is connected to VLAN2 does not have internet. However it gets an IP via DHCP from N7000. Also a laptop connected to N7000 via wWiFi can ping Nvidia Shield.