delv prints weird TTL values

Summary

The delv utility prints very large and weird-looking TTLs when the queried zone is unsigned.

BIND version used

BIND 9.14.0 (Stable Release) <id:90df20a>
running on Darwin x86_64 18.5.0 Darwin Kernel Version 18.5.0: Mon Mar 11 20:40:32 PDT 2019; root:xnu-4903.251.3~3/RELEASE_X86_64
built by make with '--prefix=/usr/local/Cellar/bind/9.14.0_2' '--enable-threads' '--enable-ipv6' '--with-openssl=/usr/local/opt/openssl' '--with-libjson=/usr/local/opt/json-c' '--with-python=/usr/local/opt/python/bin/python3' '--with-python-install-dir=/usr/local/Cellar/bind/9.14.0_2/libexec/vendor/lib/python3.7/site-packages' 'CC=clang' 'PKG_CONFIG_PATH=/usr/local/opt/json-c/lib/pkgconfig:/usr/local/opt/openssl/lib/pkgconfig:/usr/local/opt/readline/lib/pkgconfig:/usr/local/opt/sqlite/lib/pkgconfig:/usr/local/opt/xz/lib/pkgconfig:/usr/local/opt/python/lib/pkgconfig' 'PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig:/usr/local/Homebrew/Library/Homebrew/os/mac/pkgconfig/10.14'
compiled by CLANG 4.2.1 Compatible Apple LLVM 10.0.0 (clang-1000.11.45.5)
compiled with OpenSSL version: OpenSSL 1.0.2r  26 Feb 2019
linked to OpenSSL version: OpenSSL 1.0.2r  26 Feb 2019
compiled with libxml2 version: 2.9.4
linked to libxml2 version: 20904
compiled with libjson-c version: 0.13.1
linked to libjson-c version: 0.13.1
threads support is enabled

default paths:
  named configuration:  /usr/local/Cellar/bind/9.14.0_2/etc/named.conf
  rndc configuration:   /usr/local/Cellar/bind/9.14.0_2/etc/rndc.conf
  DNSSEC root key:      /usr/local/Cellar/bind/9.14.0_2/etc/bind.keys
  nsupdate session key: /usr/local/Cellar/bind/9.14.0_2/var/run/named/session.key
  named PID file:       /usr/local/Cellar/bind/9.14.0_2/var/run/named/named.pid
  named lock file:      /usr/local/Cellar/bind/9.14.0_2/var/run/named/named.lock

Steps to reproduce

Run "delv google.com mx"

What is the current bug behavior?

I see this:

; unsigned answer
google.com.		3200171710 IN	MX	10 aspmx.l.google.com.
google.com.		3200171710 IN	MX	20 alt1.aspmx.l.google.com.
google.com.		3200171710 IN	MX	30 alt2.aspmx.l.google.com.
google.com.		3200171710 IN	MX	40 alt3.aspmx.l.google.com.
google.com.		3200171710 IN	MX	50 alt4.aspmx.l.google.com.

What is the expected correct behavior?

I expect to see the correct TTL of 600 (or less) (as shown by dig):

;; ANSWER SECTION:
google.com.		295	IN	MX	50 alt4.aspmx.l.google.com.
google.com.		295	IN	MX	10 aspmx.l.google.com.
google.com.		295	IN	MX	40 alt3.aspmx.l.google.com.
google.com.		295	IN	MX	20 alt1.aspmx.l.google.com.
google.com.		295	IN	MX	30 alt2.aspmx.l.google.com.

Relevant configuration files

n/a

Relevant logs and/or screenshots

n/a

Possible fixes

don't know