Hi, this is not template issue, links are based on current location and K2 (v.2.9) wasn't perfect written, so this kinds of differences are possible. Check links from 2 areas: DOMAIN/berichte/herren6/itemlist/user/985-falkbernstein DOMAIN/itemlist/user/985-falkbernstein
I guess you should ask creators of K2 why or use 302 redirection to fix those issues.