Originally Posted by Morkl
Thanks for pointing it out. I'm fairly certain it is because the modified Reader is not allowed access to the stock Settings app's shared data, because it is signed with my key instead of Sony's. I think I'll have to provide a modified Settings app (which in turn would not work with the stock apps) to make it work but I'd love to be proven wrong.
I don't think that's to do with the key, but rather than it's installed as a different app with a different user ID.
For example, on my T1 /data/data/com.sony.drbd.ebook.reader is owned by UID 10006 (and GID 10006) but /data/data/com.sony.drbd.ebook_mod.reader is owned by UID 10046 (and GID 10006). Under /data/data/com.sony.drbd.ebook.reader there's a directory called shared_prefs and a file in there called com.sony.drbd.ebook.reader_preferences.xml and the permissions on that file are read/write for the user and group, but no access for everyone else.