Hello,

I just found this odd behavior on my Emacs and I'd like to ask how to
fix it.  I'm attaching a.c with 500 chars in. Go to the very bottom of
the file and hitting the tab will move the cursors to the right. hitting the
tab key again moves it again. It just keeps going.

If you delete some char from the file, it stop behaving.

I can reproduce this with the following Emacs with `-q`.

 - Debian Sid's Emacs 1:25.2+1-11
 - The current tip of emacs-26 branch (ea624626)

Does anyone see the behavior?

Thanks,
-- 
           yashi