It appears that two characters are being drawn in the same space.

In GNU Emacs 25.1.50.1 (x86_64-apple-darwin15.5.0, NS appkit-1404.47 Version 10.11.5 (Build 15F34))
 of 2016-07-10 built on breton.holly.idiocy.org
Repository revision: 344eb6ee66e515c812139492990001764724e506
Windowing system distributor 'Apple', version 10.3.1404
Recent messages:
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Contacting host: debbugs.gnu.org:80
Opening nndoc server on /var/folders/rs/0j9q5wvj5qv1h4p08j_dnbvw0000gn/T/gnus-temp-group-51168zC2-ephemeral...done
Error during redisplay: (widget-mouse-help #<window 58 on *Article nndoc+ephemeral:bug#3994*> #<overlay in no buffer> 575) signaled (wrong-type-argument stringp nil) [2 times]
mwheel-scroll: End of buffer [3 times]
mwheel-scroll: Beginning of buffer [13 times]
Mark set
previous-line: Beginning of buffer [2 times]
Making completion list...

Configured features:
JPEG RSVG NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS

Important settings:
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8

Major mode: Debbugs

Minor modes in effect:
  diff-auto-refine-mode: t
  magit-auto-revert-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  global-flycheck-mode: t
  show-paren-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow emacsbug gnuplot-gui gnuplot info-look rect debug epa-file
mailalias smtpmail sendmail nnir thai-util thai-word lao-util view
flow-fill tabify vc-git cc-mode cc-fonts cc-guess cc-menus cc-cmds
cc-styles cc-align cc-engine cc-vars cc-defs ibuf-ext ibuffer
ibuffer-loaddefs sh-script smie executable ob-gnuplot ob-dot ob-js
org-habit org-agenda image-file org-element org-rmail org-mhe org-irc
org-info org-gnus org-docview doc-view jka-compr image-mode org-bibtex
bibtex org-bbdb org-w3m org org-macro org-footnote org-pcomplete
org-list org-faces org-entities noutline outline org-version
ob-emacs-lisp ob ob-tangle ob-ref ob-lob ob-table ob-exp org-src ob-keys
ob-comint ob-core ob-eval org-compat org-macs org-loaddefs cal-menu
calendar cal-loaddefs linum magit-blame magit-stash magit-bisect
magit-remote magit-commit magit-sequence magit magit-apply magit-wip
magit-log magit-diff smerge-mode diff-mode magit-core magit-autorevert
autorevert filenotify magit-process magit-popup magit-mode magit-git
magit-section magit-utils git-commit help-fns radix-tree log-edit
pcvs-util with-editor async-bytecomp async tramp-sh tramp tramp-compat
tramp-loaddefs trampver shell pcomplete advice map misearch
multi-isearch shr-color color qp shr svg dom browse-url sort smiley
gnus-cite mail-extr gnus-async gnus-bcklg gnus-agent gnus-srvr
gnus-score score-mode nnvirtual nntp gnus-ml gnus-msg disp-table nndoc
gnus-cache gnus-dup gnus-art mm-uu mml2015 mm-view mml-smime smime dig
gnus-sum gnus-group gnus-undo gnus-start gnus-cloud nnimap nnmail
mail-source utf7 netrc nnoo parse-time gnus-spec gnus-int gnus-range
gnus-win gnus nnheader wid-edit mm-archive message dired dired-loaddefs
format-spec rfc822 mml mml-sec epa epg gnus-util rmail rmail-loaddefs
mailabbrev gmm-utils mailheader mail-utils network-stream starttls
url-cache crm debbugs-gnu add-log debbugs soap-client mm-decode
mm-bodies mm-encode url-http tls gnutls url-auth mail-parse rfc2231
rfc2047 rfc2045 ietf-drums url-gw nsm puny warnings rng-xsd rng-dt
rng-util xsd-regexp xml term/xterm xterm mm-util mail-prsvr unichar
exec-path-from-shell powershell-mode speedbar sb-image ezimage dframe
post derived cl abc-mode paredit go-eldoc go-mode url url-proxy
url-privacy url-expand url-methods url-history url-cookie url-domsuf
url-util mailcap find-file ffap thingatpt etags xref project compile
comint ansi-color ring geiser flycheck find-func rx subr-x dash windmove
server edmacro kmacro paren wombat-theme use-package diminish bind-key
easy-mmode finder-inf autoinsert go-mode-autoloads info package
epg-config url-handlers url-parse auth-source cl-seq eieio eieio-core
cl-macs eieio-loaddefs password-cache url-vars seq byte-opt gv bytecomp
byte-compile cl-extra help-mode easymenu cconv cl-loaddefs pcase cl-lib
time-date mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/ns-win ns-win ucs-normalize term/common-win
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese charscript case-table epa-hook jka-cmpr-hook help simple abbrev
obarray minibuffer cl-preloaded nadvice loaddefs button faces cus-face
macroexp files text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget hashtable-print-readable backquote kqueue
cocoa ns multi-tty make-network-process emacs)

Memory information:
((conses 16 698126 81959)
 (symbols 48 56643 16)
 (miscs 40 5089 1029)
 (strings 32 139370 21892)
 (string-bytes 1 4623261)
 (vectors 16 89708)
 (vector-slots 8 2047057 36584)
 (floats 8 992 1205)
 (intervals 56 6204 1338)
 (buffers 976 62))

-- 
Alan Third