If you have more than 256 flags, you run out of 8-bit characters, so you have to use another flag type to get 64k:
- UTF-8: 16-bit BMP flags
- long: two-character flags like 'AB'
- num: decimal numbers like '10234'
But our implementation for 'long' is wrong, it encodes as 'A+B', which means it cant distinguish between 'AB' and 'BA' and causes overgeneration.