Commented lines in named.conf are still interpreted

I recently found out that my domain (set up on a Trusty dedicated server) was not resolved anymore.
I didn't notice it soon enough to be sure (server not "in production" yet, it's considered a "side project"...), but I think the problem came up after an apt-get upgrade...

I did a

root@mydomain:/etc/bind# named-checkzone mydomain.tld /etc/bind/named.conf

And surprisingly got this:

/etc/bind/named.conf:1: unknown RR type 'This'
dns_master_load: /etc/bind/named.conf:3: unexpected end of line
dns_master_load: /etc/bind/named.conf:2: unexpected end of input
/etc/bind/named.conf:4: unknown RR type 'structure'
/etc/bind/named.conf:5: unknown RR type 'this'
...

Long story short: it seems the commented lines are interpreted!

Here is the original named.conf file

// This is the primary configuration file for the BIND DNS server named.
//
// Please read /usr/share/doc/bind9/README.Debian.gz for information on the
// structure of BIND configuration files in Debian, *BEFORE* you customize
// this configuration file.
//
// If you are just adding zones, please do that in /etc/bind/named.conf.local
include "/etc/bind/named.conf.options";
include "/etc/bind/named.conf.local";
include "/etc/bind/named.conf.default-zones";
//Zone domaine de test
zone "mydomain.tld" { type master; file "/etc/bind/db.mydomain.tld"; allow-transfer { trusted; wtfdns; }; allow-query { any; }; };

Is that a "new", expected Bind9 "feature"?
I tried the # and the / * ...* / methods, but none seems to work!
How are we supposed to comment things out???
And worse: if the generated files are messed up, how can we trust Bind9

I found several posts on obscure forums about the same problem, usually "solved" by removing all commented lines.

I don't want to be an a$$h01e to the guy that will inherit that, so I will need to leave comments here and there!

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.