It's in the 7.2 release notes:http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/7_x/nx-os/release/notes/72_nx-os_release_note.html#pgfId-1174959 "FEX AA featuresFabric Extender (FEX) is a pass-through/mux device designed to provide top of ...

Normal Spanning-tree process would put either Po11 or Po12 in Blocking, assuming that the N7K is the root. The VPC peer-link is ALWAYS forwarding, but that doesn't mean that both uplinks would be forwarding. Dan