Okay, got it.
Started re-reading my PR, spotted my mess 2s later. >_<".
Good(?) news: it's actually broken on *all* Kindles

. And so early that you don't get a nice crash.log.
Bad news: I also managed to mess something else up, which might also affect Kobos. I'm awesome.

.
TL;DR: Yeah, stay away from -433, even on Kobos, my bad. >_<.