FirstSection returns wrong value for taxonomy nodes

[bep]

Working on something else, I have a failing test that looks like it should not. mycategory.FirstSection shold return the categories branch, now it returns the home page.

[importhuman]

I'd like to take this up, but I'm not sure if I'm looking in the right place. Couldn't find anything with mycategory, is this the FirstSection function in page__tree.go, or the getFirstSection function in content_map.go?