A little trick that may help:
- locate a BCC file with this problem
- with a ctrl-click or right-click, select "Display Content Package" (not sure that this is the exact text as I use OS X/Finder in French but i'm sure that this is the only contextual menu item with the word "Package")
- from there, you may see different files used in this BCC document (BCC document is a package and a package is a kind of folder that looks like a file).
Here's an example of this:
"doc.thread" is the file that contains "structure", text and other data (colors […]) for this file, so don't touch it!
Other files are images used in this document. They may be pdf (as here), tiff, jpeg…
So, you may open them in Preview.app and then see if the black border problem comes from images or from the "doc.thread" file itself.
Caution, don't edit anything, don't change any file name.
Just open images in Preview and see what happens (don't hesitate to copy your file(s) before this).
Hope this helps.