On Sun, Jun 9, 2013 at 6:06 PM, Eli Zaretskii <eliz@gnu.org> wrote:

"If it hurts, don't do that." You've put window-start on a position
that is at the beginning of a line, but happens to be covered by an
overlay. Emacs obeyed.

What did you expect instead, and why? Is there some real-life use
case where this causes trouble?

I think the correct behavior would be to adjust the window-position. As far as the window is concerned, putting a hiding overlay should be no different than deleting text.

Yes, it happens quite frequently after (fold-dwim-hide-all), and maybe in similar commands.