Special characters mess up sort order

Using Views Tagadelic I have a problem with the sort order of tags when it comes to special characters. I set "Taxonomy: Term Name" as sort criteria in views which shows my tags in an alphabetical order. But: When there are tags starting with a special character (like ä, ö, ü, ß; talking about a website in german), those are listed before all the others. Example:

Categories: birnen, ananas, äpfel, obst, überfluss, absinth
Sort order (should be): absinth, äpfel, ananas, birnen, obst, überfluss
Sort order (is): äpfel, überfluss, absinth, ananas, birnen, obst

(I am not sure if german umlaute should be treated as the respective vowel+e (ä->ae, ö->oe, ü->ue) or just as a vowel (ä->a, ö->o, ü->u) when it comes to sorting. Both work.)

This doesn't happen when I create a view with a list of nodes ordered by title. For that reason I think it's a Views Tagadelic problem, not a Views problem.