Go to the website,
click on all search options
click multi-city
click use miles
set up a two segment, valid one way with a stopover
hit enter
Alaska.com returns options for a one way cash fare for the first segment only
Click change you search
you have a one segment one way with use miles not selected
click multicity, click use miles
reinsert second segment
You now get the results you want.
Come on Alaska, this has been the same repro for months!!!