Syahir Hakim,
I found a possible issue with tabs in posts (see post “Verdwenen ABP miljarden” with three tabs in page-1 on vraagde2ekamer.nl in version 1.5.6). Activating this post as a single post will not show the three panes in three tabs with the first tab activated, but shows all the text and three thumbnails as one text pane.
Furthermore, the widgets on the right side go under the posts.
Sjaak