During input processing of received frames, the commit
c7cffd65c5d858425e90b847d2e8e583e3b13bf7 (D26436) introduced a
generalized processing von 802.1q and 802.1ad frames by replacing the
VLAN header by mbuf meta data.
Unfortunately the ethertype of the original frame is lost. So if the
frame is processed by other kernel routines later (i.e. netgraph),
802.1ad frames will be indistinguishable from 802.1q frames.
In my case this breaks further processing.