If 'sort by tags' in an 'ascending' direction is used in an advanced sort then tasks without a tag are higher in the list than tasks with a tag. If a 'descending' direction is used then tasks without a tag are lower in the list than tasks with a tag.

If a user is sorting by tags, in my opinion it is the tasks with tags they are most interested in, so I think the tasks without tags should be lower in the sorted list than tasks with tags whether the sort is in an ascending or descending direction.