did you install the Community-Builder before?
If not, you can deactivate this links in Configuration Manager - General Settings ->Community-Builder -> Community-Builder Support-> no
But right, if the owner is 'null' (a category created in backend by the admin) it will result in a blank user id.
To give you an answer concerning the handling of user galleries (see your topic here
We are at the moment in developing a new structure of handling user galleries.
It will take some days...