Knot 1.5.0 gives a strange RCODE for EDNS=1 instead of BADVERS
$ dig +edns=1 ripe.net @ns2.ams.authdns.ripe.net
; <<>> DiG 9.10.0-P2 <<>> +edns=1 ripe.net @ns2.ams.authdns.ripe.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: ?256, id: 3362
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 6, ADDITIONAL: 3
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;ripe.net. IN A
;; ANSWER SECTION:
ripe.net. 21600 IN A 193.0.6.139
;; AUTHORITY SECTION:
ripe.net. 3600 IN NS ns3.nic.fr.
ripe.net. 3600 IN NS pri.authdns.ripe.net.
ripe.net. 3600 IN NS sec1.apnic.net.
ripe.net. 3600 IN NS sec3.apnic.net.
ripe.net. 3600 IN NS sns-pb.isc.org.
ripe.net. 3600 IN NS tinnie.arin.net.
;; ADDITIONAL SECTION:
pri.authdns.ripe.net. 3600 IN A 193.0.9.5
pri.authdns.ripe.net. 3600 IN AAAA 2001:67c:e0::5
;; Query time: 11 msec
;; SERVER: 193.0.0.101#53(193.0.0.101)
;; WHEN: Mon Aug 11 10:49:53 CEST 2014
;; MSG SIZE rcvd: 256