I read your blog and tried out our packaged 2.9.0 and my git build (d7bb908 Improve the way we track video playing state), and in both cases Start Slideshow just enters the new fullscreen mode, no slideshow.
When in Browse mode, selecting View|Slideshow simply makes the window go to full screen and does not do a slideshow. When in View mode, View|Slideshow behaves as expected.
Git commit b5d8fbdbfe67f31dda15641f2c7f839fef762f1f by Aurélien Gâteau.
Committed on 07/12/2012 at 15:25.
Pushed by gateau into branch 'master'.
Fix slideshow not starting
Make sure we go in view mode when started with "-" and when "Start Slideshow"
is selected from menu.
M +4 -0 app/mainwindow.cpp
(In reply to comment #2)
When we come out of slide show, does it return to the last mode (e.g. Browse) or is it then set to View? I think the former should be expected behavior.