The appearance of the icons is not right, icons are smaller, and trying to enlarge the icon view makes the icons even smaller. This is probably related to http://bugzilla.gnome.org/show_bug.cgi?id=382544 The question is, is Thunar doing something wrong or is GtkIconView broken?
Well, Thunar uses ExoIconView, which is a GtkIconView subclass. So it's perfectly possible that ExoIconView makes some assumptions about GtkIconView that aren't valid anymore, causing the problem. If GtkIconView supported single-click activation, I'd say we should just drop ExoIconView entirely (pretty sure that's the only advantage ExoIconView has anymore).