The unsafeToBreak flag is incorrectly calculated as bit 1: https://hackage.haskell.org/package/harfbuzz-pure-1.0.3.1/docs/src/Data.Text.Glyphize.Buffer.html#GlyphInfo

Should be bit 0.

The other flags are also off by one, see: https://github.com/harfbuzz/harfbuzz/blob/07f2d8d5384943445ca00c0e127de81d37539e65/src/hb-buffer.h#L161