1. On unix-like OS visit https://en.wikipedia.org/wiki/Paul_Erdős in firefox
2. Copy its link
3. Paste it with mouse wheel. Result: Paul_Erd\u0151s
4. Paste it with M-x clipboard-yank. Result: Paul_Erdős

The bug is confirmed by independent user here:
http://emacs.stackexchange.com/questions/13472/pasting-unicode-from-external-applications-with-mouse-wheel-on-unix?noredirect=1#comment20167_13472



In GNU Emacs 25.0.50.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.8)
 of 2015-05-19 on lcy01-07
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description:    Ubuntu 14.04.1 LTS

Configured using:
 `configure --build=x86_64-linux-gnu --prefix=/usr
 '--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
 '--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
 '--libdir=${prefix}/lib/x86_64-linux-gnu'
 '--libexecdir=${prefix}/lib/x86_64-linux-gnu' --disable-maintainer-mode
 --disable-dependency-tracking --prefix=/usr --sharedstatedir=/var/lib
 --program-suffix=-snapshot --with-x=yes --with-x-toolkit=gtk3
 'CFLAGS=-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat
 -Werror=format-security' CPPFLAGS=-D_FORTIFY_SOURCE=2
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Text

Minor modes in effect:
  csv-field-index-mode: t
  diff-auto-refine-mode: t
  TeX-PDF-mode: t
  tabbar-mwheel-mode: t
  tabbar-mode: t
  helm-mode: t
  shell-dirtrack-mode: t
  async-bytecomp-package-mode: t
  ido-everywhere: t
  cua-mode: t
  global-auto-revert-mode: t
  global-subword-mode: t
  subword-mode: t
  recentf-mode: t
  global-whitespace-mode: t
  show-paren-mode: t
  delete-selection-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t

Recent messages:
Mark set [2 times]
Undo!
Mark set [2 times]
next-line: End of buffer
Mark set [2 times]
Undo!
Mark set [3 times]
Buffer new<6> modified; Do you want to save? (y or n) n
mwheel-scroll: Beginning of buffer [4 times]
Mark set [3 times]

Load-path shadows:
/usr/share/emacs/site-lisp/rst hides
/usr/share/emacs/25.0.50/lisp/textmodes/rst
/usr/share/emacs/site-lisp/dictionaries-common/ispell hides
/usr/share/emacs/25.0.50/lisp/textmodes/ispell
/usr/share/emacs/site-lisp/dictionaries-common/flyspell hides
/usr/share/emacs/25.0.50/lisp/textmodes/flyspell

Features:
(shadow mail-extr emacsbug message rfc822 mml mml-sec mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mail-utils winner csv-mode sort
jka-compr eieio-opt speedbar sb-image ezimage dframe find-func misearch
multi-isearch vc vc-dispatcher markdown-mode noutline outline server
vc-git diff-mode bk-misis-minor-mode bk-canvas-minor-mode
bk-pentadactyl-mode lib-gnrl rect lib-bk-TeX latex tex-style tex dbus
crm lib-bk-rst rst lib-bk-py python-mode derived info-look flymake cl
cc-cmds cc-engine cc-vars cc-defs lib-bk-org lib-bk-math two-column
lib-bk-gnrl lib-bk-bash buffer-extension iso-transl hippie-exp help-mode
dired+ image-file tabbar ibuffer helm-mode helm-files rx image-dired
tramp tramp-compat tramp-loaddefs trampver shell pcomplete format-spec
dired-x dired-aux ffap thingatpt helm-buffers helm-elscreen helm-tags
helm-bookmark helm-adaptive helm-info bookmark pp helm-locate helm-help
helm-match-plugin helm-grep helm-regexp helm-plugin grep helm-external
helm-net browse-url xml url url-proxy url-privacy url-expand url-methods
url-history url-cookie url-domsuf url-util url-parse auth-source
gnus-util mm-util mail-prsvr password-cache url-vars mailcap helm-utils
dired compile comint ansi-color ring helm easy-mmode cl-macs helm-source
cl-seq eieio-compat eieio byte-opt gv bytecomp byte-compile cconv
eieio-core helm-config helm-easymenu edmacro kmacro async-bytecomp
advice help-fns async helm-aliases ido cua-base sh-script smie
executable autorevert filenotify cap-words superword subword recentf
tree-widget disp-table whitespace cl-extra seq paren delsel cus-edit
cus-start cus-load wid-edit cl-loaddefs pcase cl-lib finder-inf tex-site
info easymenu package epg-config time-date mule-util tooltip eldoc
electric uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win
term/common-win x-dnd 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 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 case-table epa-hook jka-cmpr-hook help simple abbrev
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 dbusbind gfilenotify
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 449847 30693)
 (symbols 48 44192 0)
 (miscs 40 1965 794)
 (strings 32 100958 16873)
 (string-bytes 1 3239770)
 (vectors 16 44335)
 (vector-slots 8 1564190 208828)
 (floats 8 343 532)
 (intervals 56 7067 69)
 (buffers 976 24)
 (heap 1024 71572 2841))