1) Assign a group 'Administer Categories' and 'Access Feeds' permission. (say group1)
2) Create a user in group1 (say user1)
3) Log in via user1
4) Go to 'Admin -> Properties'
5) Edit a 'Category Field' by updating/adding a property
6) Save the edit
The category field update is saved. However, since that page also has 'Feed Fields' on it, UI throws an exception An unexpected error occurred Not authorized to perform the action: Administer Feeds. This is misleading since the user is not trying to perform any feed-related admin operation and also because the category field edit gets saved.