After updating using freebsd-update from 9.2p8 to 10.0p4, one has to reboot after the first freebsd-update install. If one does, ifconfig can't handle the new devices, so the system was only reachable via console. Dangerous for a remote upgrade... After the second freebsd-install, ifconfig worked again.
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Make a second try for a different host, this time the reboot worked and the ifconfig binaries did not have the problem. I'll make further tests and give feedback.
Further tests showed that this is not a general problem.