I've just found out that a fake registration causes a few other problems (on 5.8.5 at least):
- Navigation in any book is virtually impossible. The swipe-up navigation menu doesn't show, and the Go To menu only displays the Notes tab, not the Contents tab. So you're left with flipping the pages one by one.
- Dictionaries disappear; they are not shown in the documents list, and lookup is not possible.
As soon as I delete /var/local/java/prefs/reginfo and reboot, navigation and dictionary lookup work again. Annoying.
Also, as soon as I switch WiFi on, the Kindle deregisters until a reboot even if the reginfo file is immutable. If I prevent connections to Amazon using iptables, the WiFi connection is immediately disconnected, preventing the use of WiFi e.g. for local SSH connections.
Amazon really seem to go to some lengths to force users to register.