I have seen similiar behaviour with L2 VPNs terminating on VM. Have a look Security Policy of your vSwitch or Port Group that might get involved.
Problem here is that there will be a frame comming from the VM but with MAC not assosiated with the VM itself.
The problem was related to the vswitch promiscuous mode that was disabled. Enabling the promiscuous mode everything works like a charm.
Thanks a lot for the hint!