Question about the commercial DVDs

[taras-wizard.livejournal.com]

Maybe some who's more knowledgable about the anime scene and business can answer this question.  So earlier this spring I was able to pick up on sale Bandai's DVD last volume of Scrapped Princess, and previous to my owning the DVD I had only seened the series in dubbed format; FYI, I will watch both dubbed and subtitled versions of things it's not all one or the other for me.  Regarding Symphony of those who Protect, series's last episode, so not only did Bandai dub in English voice actors in place of original dialogue, but they dubbed in new music, and what's up with that?  AFAIK, it's music that's found in the series it's not found in the parts of the last episode where Bandai has put it.

To you anime veterans this must sound like a pretty naive question, but I've not noticed in other things.