Paramiko sees connection as successful but actually fails

We are using paramiko to connect to a 'blackbox' that runs a linux variant (CentOs?) with openssh, when connecting with a non existent username the keyboard-interactive authentication is seen as successful by both openssh and paramiko, but openssh sees it as a failed connection due to the remaining response.

Extract of ssh -v testhost -l fakeuser

...
debug3: authmethod_is_enabled keyboard-interactive
debug1: Next authentication method: keyboard-interactive
debug2: userauth_kbdint
debug2: we sent a keyboard-interactive packet, wait for reply
debug3: Wrote 100 bytes for a total of 2417
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 1
Password:
debug3: packet_send2: adding 32 (len 21 padlen 11 extra_pad 64)
debug3: Wrote 84 bytes for a total of 2501
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 0
debug3: packet_send2: adding 48 (len 10 padlen 6 extra_pad 64)
debug3: Wrote 84 bytes for a total of 2585
debug1: Authentication succeeded (keyboard-interactive).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug1: Requesting no-more-sessions@openssh.com
debug1: Entering interactive session.
debug3: Wrote 136 bytes for a total of 2721
debug2: callback start
debug2: client_session2_setup: id 0
debug2: channel 0: request pty-req confirm 1
debug1: Sending environment.
debug3: Ignored env MANPATH
debug3: Ignored env HOSTNAME
debug3: Ignored env TERM
debug3: Ignored env SHELL
debug3: Ignored env HISTSIZE
debug3: Ignored env SSH_CLIENT
debug3: Ignored env QTDIR
debug3: Ignored env QTINC
debug3: Ignored env SSH_TTY
debug3: Ignored env USER
debug3: Ignored env LS_COLORS
debug3: Ignored env MAIL
debug3: Ignored env PATH
debug3: Ignored env PWD
debug3: Ignored env JAVA_HOME
debug3: Ignored env EDITOR
debug1: Sending env LANG = en_US.UTF-8
debug2: channel 0: request env confirm 0
debug3: Ignored env HISTCONTROL
debug3: Ignored env KRB5CCNAME
debug3: Ignored env SHLVL
debug3: Ignored env HOME
debug3: Ignored env LOGNAME
debug3: Ignored env QTLIB
debug3: Ignored env CVS_RSH
debug3: Ignored env SSH_CONNECTION
debug3: Ignored env LESSOPEN
debug3: Ignored env G_BROKEN_FILENAMES
debug3: Ignored env _
debug3: Ignored env OLDPWD
debug2: channel 0: request shell confirm 1
debug2: fd 3 setting TCP_NODELAY
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug3: Wrote 460 bytes for a total of 3181
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
Access Denied
debug2: channel 0: rcvd eof
debug2: channel 0: output open -> drain
debug2: channel 0: obuf empty
debug2: channel 0: close_write
debug2: channel 0: output drain -> closed
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype eow@openssh.com reply 0
debug2: channel 0: rcvd eow
debug2: channel 0: close_read
debug2: channel 0: input open -> closed
debug2: channel 0: rcvd close
debug3: channel 0: will not send data after close
debug2: channel 0: almost dead
debug2: channel 0: gc: notify user
debug2: channel 0: gc: user detached
debug2: channel 0: send close
debug2: channel 0: is dead
debug2: channel 0: garbage collecting
debug1: channel 0: free: client-session, nchannels 1
debug3: channel 0: status: The following connections are open:
  #0 client-session (t4 r0 i3/0 o3/0 fd -1/-1 cfd -1)

debug3: channel 0: close_fds r -1 w -1 e 6 c -1
debug3: Wrote 36 bytes for a total of 3217
debug3: Wrote 68 bytes for a total of 3285
Connection to testhost closed.
Transferred: sent 2984, received 2704 bytes, in 0.7 seconds
Bytes per second: sent 4292.8, received 3890.0
debug1: Exit status 117

Extract of versions from paramiko logs:

DEB [20180531-11:35:44.125] thr=1   paramiko.transport: starting thread (client mode): 0xcba48c18
DEB [20180531-11:35:44.125] thr=1   paramiko.transport: Local version/idstring: SSH-2.0-paramiko_2.2.1
DEB [20180531-11:35:44.357] thr=1   paramiko.transport: Remote version/idstring: SSH-2.0-OpenSSH_6.6.1

Blackbox (testhost) running OpenSSH_6.6.1 and target of ssh connection
Paramiko v2.2.1 source of ssh connection and gets seen a successful
Linux Red Hat 6.x host alternate source of connection using OpenSSH_5.3p1 and sees it as failed

I've also raised a case with the 'blackbox' vendor to see why it gets returned a successful, but thought I'd raise it here as well given the difference in behaviour with openssh

Start by comparing Paramiko 2.2.1's keyboard-interactive authentication behavior with the supplied OpenSSH trace and the vendor's response. Done means the differing success and failure results are reproducible and the connection outcome is handled consistently.