shaft, 
The #DNS client #drill handles EDE in a funny way : it dumps the extra text in hexadecimal and then a decoded version.
It is funny because the EXTRA-TEXT field is clearly defined as a UTF-8 encoded field (RFC 8914 section 2).
I guess that @nlnetlabs are so used to handle text field just defined as binary stuff (eg TXT records) that they did not pay attention to that :')
$ drill -D dnssec-failed.org
;; ->>HEADER<<- opcode: QUERY, rcode: SERVFAIL, id: 24
47
...
; EDE: 6 (DNSSEC Bogus): 76 61 6c 69 [...] (validation failure [...])