Voyager-xbmc/xbmc — comment on commit 8a5e3cc7a49fb03a5b0fad400d245a4e3e455bfb
File:  line 0
By Voyager-xbmc:

it depends - the whole point of resume dvd is to allow restart to be false (= resume). It works relatively well, but I agree it's messy.
So the following scenarios happen:
a) stub - disc never resumed (restart = true). stub starts disc, now stub gets to track the progress. --> wrong.
b) stub - disc resumed before and dialog window selected that we want to resume (so restart = false). now disc (via unique ID) gets to track the progress --> correct.
Hence the point of the fix.