master pages missing

Hi, 

So I wanted to edit some master pages in a new document. Usually, when you open the pages (Seiten) tab, it also opens a small window displaying all master pages. In this document however, it doesn't do that. Even if I close the tab and open it again, I can't find a display of my master pages (like in the small screenshot). It looks like the screenshot I've attached (large screenshot). 

Can yomebody help me with this problem?