I am running both wired Powerline adapters and a wireless Homegroup network and this seems to generate IP address conflicts
Yes, IP address conflicts can certainly be a problem. Common causes of IP address conflicts are:
- More than one device being manually assigned the same static IP address
- Devices getting dynamic IP addresses (via DHCP) when there are more than one DHCP server on the network
The multiple DHCP server problem can often inadvertently arise if you have more than one broadband router, wireless router, powerline router, etc. on your network. Typically all such box manufacturers now implement a DHCP server, and it is usually turned on by default...
It was only when I tried a rather odd suggestion to disable the IGMP setting in my router that everything came good.
That makes sense too. IGMP is a protocol used for managing routing of UDP multicast messages between different segments of a network. And the UPnP device discovery process (NOTIFY alive / NOTIFY bye-bye messages) is engineered using UDP multicast messages. So if IGMP is "messing" with the routing of multicast messages between segments of your network, this could certainly mess up UPnP too. As in the case above, the issue is particularly likely to happen if you have more than one broadband router, wireless router, powerline router, etc. on your network. Because each such box probably represents a different network segment, and so inter segment routing becomes an issue.
For "normal" people who have just one combined broadband plus wireless router, none of the above should be a problem. Because a) you have only one DHCP server, and b) you only have one network segment for multicasting.