Hi Martin!
What I found out is, that latest version of Wireshark doesn't work correctly with this part of code. I don't know what has been changed in the last versions, but I tried with 0.99.5 and it works well.
The Multicast stream options checks for multicast streams by comparing the first 3 bytes of destination MAC address: if it equals to 01:00:5e, then the packet is recognized as multicast packet. Your packets fit well inside this rule.
I don't know what is wrong, could be something with the tap system, I will try to check. Meanwhile you can use one older version.
Miha