There's a line called "Wikitext verwendet Markup und du kannst jederzeit eine Vorschau des Ergebnisses anzeigen." (Dunno how it's in english), that is utterly wrong. It's not a preview, it's just a switch to VE, and that's something completely different. Especially as there is a special button for switching to VE.
Either change the text (not preferred) or use a proper preview there, without VE.