I'm assuming this is simply a bug in the version of tar that ships with the kindle (i.e. busybox). I admit I also wasn't expecting it to work
Semi-serious: Yeah, maybe I should have kept this back until Amazon fixed one of the holes, only to reveal the next. But then again, I found it useful, if only to help folks like MatzeMatze or others who inadvertently bricked their devices. And I mostly believe in full disclosure anyway.
That said, it would be *really* nice if Amazon realized that allowing users to tamper with their devices (at own risk of course), instead of trying to lock them in, can actually be an advantage.
For example, I'm running a (quite old) Linksys 54 Wifi router here, which I bought specifically because there was a possibility to install OpenWRT on it. After that model became hugely popular, Linksys actually released *two* versions of the successor device: one with proprietary software, and one (I think it was called WRT54GL or so) with a Linux OS which was from the beginning designed to be modded by interested people. And it was a big success.