Recipe:
  emacs -Q
  M-x toggle-truncate-lines RET
  ; Visit the attached file
  Type: C-s t l s . c C-s C-s


After the third 'C-s', the cursor is again over the original matching
word but we can't see it.  Emacs should do horizontal auto-scrolling
during Isearch, just as it does vertical auto-scrolling.

In GNU Emacs 25.0.50.5 (i686-w64-mingw32)
 of 2014-11-23 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.3.9600
Configured using:
 `configure --without-dbus CPPFLAGS=-I/mingw32/include'

-- 
Dani Moncayo