On http://phd.martin-krafft.net/wiki/tag/factors/ideology/, another symptom of this problem can be seen: the page collects pages linking to tag/factors/ideology, and /factors/language is one of those. However, the link points to tag/factors/language, which does not link to tag/factors/ideology.

I think this is an artefact of the intersection of ikiwiki LinkingRules with the use of a page's basename when its path relative to the wikiroot should be used.