Why not have the import have an option for not adding the ending?
That's a good idea. I'll add that to my request.
The time signature may be a related to Peter's dialog on the topic of Swing/triplets beats vs straight feel.
I think there are two things at play here - first, Band-in-a-Box will always display 12/8 as 4/4, and second, there's a big difference between "importing" a MusicXML file and "opening" a MusicXML file. Importing assumes you want to keep whatever's already in your song (key, time sig, notation on other tracks, etc), where opening a MusicXML from the Open Special menu opens it as a fresh song. From the sounds of it, you're importing the MusicXML - try opening it from File > Open Special > Open MusicXML File.
If I recall, some had some chord spelling issues with Maj 7, I think as well.
As far as I can tell that's been fixed.