page title on archive missing e.g. Category: Test

The title says all I hope, when I list blog post of a categorie I get a page title/header like:
Categorr: name_of_category
Same is true for tags I would guess. Using the wiki i get no title/header when listing the wikis for a certain category or tag.

Guess this is an easy fix as there should be only a variable missing for the template, right?

Cheers, Alex