in WordPress (under settings-permalink) I saved the premalink settings again but without any effect on the problem.
I checked the URLs of the links in the inner page menue (appaerance-customize-menus-inner page menue): It starts with http://…. When I copy the link into firefox they jump to the right section. But when I use the links of inner page menue firefox doesn’t show http://….. and the link doesn’t work correctly as described above.
Hope this helps?