I started to do some research and I found this post from the developer of my chosen file manager, FX:
Then, while getting ready to post this, I found another related thread:
I thought this was a big enough deal to warrant a new thread here. Bottom line is you may want to hold off on this update, or at least go in with your eyes open because for a lot of people, like me, this is a BIG problem. It's damned near a dealbreaker for using my S4 as a matter of fact. Note that it does seem you're able to use the My Files app, but that's almost useless to me: FX has SMB support and I'm constantly pulling files off my server. I even have FolderSync set up to run every night, but I don't expect that'll work either (I'm about to try now).
Whether Samsung spits out a fix quickly, or whether I can root and fix this, it's a pretty significant problem. Be aware folks!