I added a new Activity category named "Class Features", and then added a new Activity section named "Magus", into which I added an activity and then favorited it. This is what I ended up with:
Attachment 58873
It didn't propogate the name of the section "Magus", and it added a second section. Neither of which I can change or edit in any way, even if I hit the edit button in the lower right. I've also tried exiting out of the campaign and reloading, same thing. No extensions loaded.
I did renumber/reorder all the categories, but Favorites is still 00, in case that matters. I can send you the db.xml if you want.
EDIT: I tried a "Rebuild PC feat, feature, and item activities" and it left the new category and section there, but deleted the activity. The section under Favorites is still named "-", but the extra section is gone now.
EDIT2: And after I rebuilt the activity and favorited it, it did not appear in the Favorites section.