Strange behaviour of widgets

The display of widgets on blog-views (posts) in "Catch Everest Pro" doesn't work as intended. I can't get the theme to display content in the Sidebar on pages with a single post – neither in the "Main Sidebar" nor in one of the "Optional Sidebars". Although I assigned different widgets to the "Main Sidebar", the "Optional Page Sidebar" or the "Optional Page Sidebar" the sidebar stays empty. It shows a blank white column. Unfortunately List-, Archive- and Homepage-Sidebars are doing the other way around: As default the theme displays as search- and an archives-widget on these kind of views – even if there is no widget assigned in the backend. As soon as I do so the defaults get replaced by the new widget - and come back when I reverse the assignment. It seems there is no possiblity to get an empty Sidebar on List-, Archive- and Homepage. How can I fix this issue? I already deactivated all plugins and reinstalled the theme. Same behaviour as before.