I apologise for the delay in my reply.
By physically unplugging the cable to NIC 2 on the host and configuring port mirroring on the switchport facing NIC 1 of the host I was able to confirm that the VMWare host is transmitting frames out NIC1 that have a destination MAC address of one of it's own VM's.
After carefully reviewing the captured data I noticed that the destination MAC address of the erroneous frames '02:bf:cb:50:a2:76' actually belonged to 'Local Area Connection 1' of one of my Windows 2003 server VM's housed on the suspect host.
Digging a little deeper I discovered that this virtual NIC is presented to the operating system as
Name: Local Area Connection 1
Type: VMware Accelerated AMD PCNet Adapter"
MAC: 02-BF-CB-50-A2-76
But the configuration of the VM in vCentre is
Name: Network adapter 1
Type: Flexible
MAC: 00:0c:29:fa:e8:83
Note the different MAC addresses.
Upon digging a little deeper I have discovered that the Windows 2003 server has Network Load Balancing configured on "Local Area Connection 1" and NLB is the cause of the altered MAC address.
Rather than investigate further I have simply placed a linux load balancer in front of the windows 2003 server cluster and have disabled NLB.
However I suspect there is still a fundamental problem in the VMware Virtual Switch with the way it learns MAC addresses of it's VM's using flexible vNICS. In particular with any VM which uses some form of MAC address override like that used by NLB.