bug#25855: 25.1; garbage display by raise display specification

[Eli Zaretskii]

> From: ynyaaa@gmail.com
> Date: Fri, 24 Feb 2017 15:09:43 +0900
> 
> Evaluating the form below, emacs displays garbages at the leftside of
> the window. Switching to another buffer and switching back will display
> other garbages.
> 
> (insert (propertize (make-string 100 ?\n) 'display '(raise 1)))

What did you expect to see from 'raising' the newlines?  A newline has
no glyph on display, so there's nothing to raise.

IOW, why is this not the expected behavior?