I've noticed a couple of things on my new Nexus 7 with android 4.3:
I can't read the *apk.gz files Titanium Backup creates in its backup directory (I wanted to copy the backup dir to my host computer). I get permission denied, but "ls -l" shows all the files as -rw-rw-r- access. Even if I su to root, I can't read them.
I was using rsync to copy some files from my host computer to the Nexus 7, and rsync gets errors trying to set the time on the files to make them the same time as the source files (it does copy the files though, so it had access to do that).
This all seems like it might be some new security features (some kind of new ACL maybe), but I haven't been able to find any hint of what is actually going on here. Does anyone know?