Kerning that shows up in KO not getting written when KO run

[tiro_j]

I am trying to use KO to generate kerning for a couple of specific glyphs in a font. This is an unencoded variant form (a UCAS final ring character lowered to be baseline as used in the Beaver Dene language), and a ligature involving this and another, grave-like final sign. These glyphs is accessed via a stylistic set feature in the font.

When I start up KO, I can preview automated kerning of this glyph based on my existing models, as shown in the first screenshot below.

But when I run KO to generate kerning for the font, no kerning for these glyphs are written (as shown in the second screenshot below). I have tried increasing the kerning data file size, but so far no setting I have tried has triggered inclusion of this kerning in the output.

[tiro_j]

If I define models including these glyphs, the models get written to the kerning output, but no other kerning for them.

[tiro_j]

Aha! If I increase the kerning data size to 100kb, then these glyphs get kerning.