I belive the problem is the UNLIGHTED version of that cover shorts the Kindle's cover light output if the hooks are the old black coated metal ones and are worn. Apparently older versions of it had the hooks mounted to the same metal plate in the spine without any electrical isolation (DOH!!!!) so when the black paint wore off the trouble started. The general consensus seems to be that removing the K3 from the offending cover and possibly rebooting as well resolves the problem.
The LIGHTED cover uses the two gold hooks as electrical contacts for the LED supply so they are seperate and unless its badly damaged, they wont short out the K3.
I acquired one (used) just after Christmas and so far have had no issues whatsoever. There's just enough clearance for a thin silicone skin on the K3, but YMMV as a thicker, better quality skin certainly wouldn't fit without straining the hooks.
More details of the problem in a Amazon forum topic
[here].