What happened:

Reply for the SRV resource record squashed uppercase characters in the query

What you expected to happen:

Reply should have preserved case in the query

How to reproduce it (as minimally and precisely as possible):

Corefile:

. {
    log
    errors
    auto {
        directory ...
        reload 2s
    }
}

Zone:

$ORIGIN home.arpa.
$TTL 5
@ IN SOA @ nobody.invalid. 8 3600 1200 604800 5
     NS @
     AAAA ...
_smb._tcp PTR Home\ Media._smb._tcp
Home\ Media._smb._tcp SRV 0 0 445 samba

$ dig @... -t PTR "_smb._tcp.home.arpa."
;; QUESTION SECTION:
;_smb._tcp.home.arpa.		IN	PTR

;; ANSWER SECTION:
_smb._tcp.home.arpa.	5	IN	PTR	Home\032Media._smb._tcp.home.arpa.

$ dig @... -t SRV "Home Media._smb._tcp.home.arpa."
;; QUESTION SECTION:
;Home\032Media._smb._tcp.home.arpa. IN	SRV

;; ANSWER SECTION:
home\032media._smb._tcp.home.arpa. 5 IN	SRV	0 0 445 samba.home.arpa.

Anything else we need to know?:

RFC 6763, Section 4.1.1:

The portion of the Service Instance Name is a user-
friendly name consisting of arbitrary Net-Unicode text [RFC5198]. It
MUST NOT contain ASCII control characters (byte values 0x00-0x1F and
0x7F) [RFC20] but otherwise is allowed to contain any characters,
without restriction, including spaces, uppercase, lowercase,
punctuation -- including dots -- accented characters, non-Roman text,
and anything else that may be represented using Net-Unicode.

Environment:

• the version of CoreDNS: 1.22