I have had transparency issues in SW 2015. I would change the transparency of a single face/surface and then not be able to make it opaque again without making the part opaque. I think there are a couple of ways to changing transparency, right click the face or go through the menus and no matter what I tried, it would do funky unexpected stuff.
Sorry, I never found a solution except not to use it and keep my sanity. I guess I might have switched to using the appearance transparency, this way you can set the percentage.