bug#25906: 25.1; strange behavior of overlapped mouse-face

[ynyaaa]

Evaluating the form below, then move the mouse cursor on the inserted text.
When it is on aaa, underline is displayed on aaaBBB as expected.
When it is on ccc, overline is displayed on BBBccc as expected.

When it is moved holizontally from aaa to BBB, overline is not displayed.
When it is moved holizontally from ccc to BBB, underline is not displayed.
When it is moved onto BBB vertically from upside or downside,
both overline and underline are displayed on BBBccc.

(let ((p (point))
      ol-1 ol-2)
  (insert "<aaaBBBccc>\n")
  (setq ol-1 (make-overlay (+ p 1) (+ p 7))) ;; on aaaBBB
  (overlay-put ol-1 'mouse-face '(:underline t))
  (overlay-put ol-1 'evaporate t)
  (setq ol-2 (make-overlay (+ p 4) (+ p 10))) ;; on BBBccc
  (overlay-put ol-2 'mouse-face '(:overline t))
  (overlay-put ol-2 'evaporate t))




In GNU Emacs 25.1.1 (i686-w64-mingw32)
 of 2016-09-18 built on LAPHROAIG
Windowing system distributor 'Microsoft Corp.', version 6.0.6002
Configured using:
 'configure --host=i686-w64-mingw32 --without-dbus
 --without-compress-install CFLAGS=-static'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS

Important settings:
  value of $LANG: JPN
  locale-coding-system: cp932

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-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
  line-number-mode: t
  transient-mark-mode: t

Recent messages:

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils help-fns
mule-diag apropos benchmark rect misearch multi-isearch debug kmacro
two-column iso-transl help-mode easymenu cl-loaddefs pcase cl-lib
time-date mule-util japan-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table
w32-win w32-vars 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 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 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 w32notify w32 multi-tty
make-network-process emacs)

Memory information:
((conses 8 107085 23454)
 (symbols 32 31013 0)
 (miscs 32 226 320)
 (strings 16 45273 5127)
 (string-bytes 1 1001128)
 (vectors 8 14127)
 (vector-slots 4 559411 5188)
 (floats 8 185 387)
 (intervals 28 1427 832)
 (buffers 520 25))