In the user preference table, there are records with name vtb.sort_by and the value is either name or sys_updated_on
This is due to the sort option present on the $vtb.do page.
On the top right corner of this page, there is a sort by options which has two values Name and recent activity.
Depending on the value of the sort the user preference will be updated for that particular user.
For more information on user preference please go through the below documentation.