When I start emacs with:

  emacs -Q -eval '(insert-char ?x 80)'

then, as expected, all the Xes are displayed in one line and the cursor
is displayed in the right fringe.

But when I start it with:

  emacs -Q -eval '(set-fringe-mode (cons 0 8))' -eval '(insert-char ?x 80)'

then two lines are used, the last column of the first line is empty, an
arrow appears in the right fringe, and the cursor is displayed in the
second column of the second line.  See attached screenshot.

The second case should be displayed almost like the first with all Xes
in one line.