Permanently added hostkeys (due to IP address pool), without confirmation

[Steffen Nurpmeso]

Hello,

maybe someone could please help and shed some light on a problem
that i don't understand, and that even in multiple ways.
The problem occurred three or four times over the past months
(maybe half a year?) and manifests as

  ++ Pushing to "gitlab" (at least "master" differs)!
  Warning: Permanently added the RSA host key for IP address '104.46.105.89' to the list of known hosts.

I get no confirmation prompt, which i normally do?!
Of course i do have a configuration file with an

  UserKnownHostsFile        ~/arena/data/ssh/known_hosts

entry, and that already has a

  gitlab.com,54.93.71.23  DATA

line for months.  I do have a "Host" entry for "*gitlab.org" (with
explicit IdentityFile).  The entry in known_hosts that i (hope to
have confirmed correctly back then) is not identical with the
other two entries, but which are, except for the addresses

  --- k.1 2015-10-09 18:09:10.511793883 +0200
  +++ k.2 2015-10-09 18:09:26.508373888 +0200
  @@ -1,2 +1,2 @@
  -52.21.36.51
  +104.46.105.89
   ssh-rsa ...

I understand that the keys in k.1 and k.2 are the same that
ssh-keyscan(1) gives me, whereas the address i verified does
currently give no ssh-keyscan result at all.  (I verified it back
in the day in that i was able to login after placing my public key
at their server via a HTTPS connection after i had created my
account.  I'm no expert in mathematics or the SSH protocols, but
i'm confident as only a greenhorn or real expert can be.)

So: no confirmation prompt, no hostname but only the address for
the entry in known_hosts even though the connection is to
gitlab.com (they're appended though), and multiple entries with
the same key.
I'm on "OpenSSH_7.1p1, OpenSSL 1.0.2d 9 Jul 2015".
Thank you in advance for any hint, ciao,

--steffen