ah ok i think i have a better test case to trigger what i was talking about:
^s ^d -n17 +4* ^d -* +4*
this plays two doubles of a low b (-1) and fsharp (+4). the second double is missing the b when ditto is used. it seems like going negative is tricking something. using n17 on the second double works.
if you switch the notes, the b isn't played at all!
^s ^d +4n17 -*
but if you do:
^s ^d +4n17 -* -*
(ie. playing the low b individually after the double) even that is wrong. it sounds like a +4-*