@Barty: The keyword here being "k3". A whole 'nother beast than the K5

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Although it did suffer from the exact same kind of issues, the impact, as you said, was limited to disrupting the UI at worse. (And the workaround was already the same: use a vanilla freetype build).
Hence my numerous warnings on both the K2/3/4 & K5 fonts hack docs. The issue is exacerbated with the K5 (and particularly the PW, since we can't kubrick it) because of the inability to recover from the 'Your Kindle Needs Repair' (YKNR) screen with a vanilla/nearly-vanilla device without resorting to opening it up, unlike the previous models, where the recovery was more easily accessible and/or a hard factory reset was a possibility.