On the widgets page I have dragged widgets into the primary and secondary widget areas and they appear on all pages except the posts page and on category pages.
I have tried to temporarily reset the posts page to another and the problem moves to that page.
I have tried to temporarily reset the theme to 2010 and the problems disappear.
I've tried two conditional widget controllers (i.e. forcing widgets to appear on certain pages only) but they face the same problem.
Is there a setting somewhere that I've overlooked or is there another explanation?