Avast using UPD destination Port 0 in VMWare

Avast Free Antivirus / Premium Security
1

I installed the latest Avast in a WinXP Pro SP3 VMWare guest, hosted on WinXP Pro SP3.
I have the same firewall in both the guest and the host and I’m using VMWare nat translation.

After installing Avast 5, and setting up new TCP rules to allow it to update properly, the host firewall reports connections to

And all using a destination port of UDP Port 0 (zero).

Interestingly, the firewall on the guest does not report these (and it has the same rules).

Is this expected behavior? What might it be doing?

Avast 5.0.462
VMWare Player 3.0.1

Thanks.