Case sensitivity of RDATA in PTR records

Is a DNS server expected to preserve the case of domain names in resource record data of PTR records.

As per RFC 4343 - Domain Name System case insensitivity clarification<http://tools.ietf.org/html/rfc4343>, section 4 says -
While ASCII label comparisons are case insensitive, [STD13<http://tools.ietf.org/html/rfc4343#ref-STD13>] says case MUST be preserved on output and preserved when convenient on input.

But RFC RFC2535 - Domain Name System Security Extensions  section 8.1 says -
8.1 Canonical RR Form

   For purposes of DNS<http://www.bind9.net/rfc> security, the canonical form for an RR is the
   wire format of the RR with domain names (1) fully expanded (no name
   compression via pointers), (2) all domain name letters set to lower
   case, (3) owner name wild cards in master file form (no substitution
   made for *), and (4) the original TTL substituted for the current
   TTL.

RFC 3597 mentions
DNSSEC<http://www.dnssec.net/> Canonical Form and Ordering

   DNSSEC<http://www.dnssec.net/> defines a canonical form and ordering for RRs [RFC 2535<http://www.rfc-archive.org/getrfc.php?rfc=2535>]
   (section 8.1).  In that canonical form, domain names embedded in the
   RDATA are converted to lower case.

Are these standards contradicting vis-à-vis case (in)sensitivity of domain names. Or is the canonical form definition only  for constructing SIG RRs as mention in RFC 2535 section 8 -
"A canonical form and ordering within an RRset is necessary in consistently constructing and verifying SIG RRs"

Thanks,
Prasad

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