If one executes the following in a graphical frame, the line will break:
(insert (propertize
"\n"
'display `(space :align-to (- right))
'face '(:underline t))
"\n")
(toggle-word-wrap 1)
If one makes the line one pixel shorter, it will work fine.
(insert (propertize
"\n"
'display `(space :align-to (- right (1)))
'face '(:underline t))
"\n")
(toggle-word-wrap 1)
Evgeni