Composite glyphs .sc and .cap

I’m following up on an issue I previously noted. By adding slots, I create a.sc, gravecomb.sc, acutecomb.sc, circumflexcmb.sc, etc. To make them immediately visible, I "dirty" the glyphs. I create anchors and the corresponding class in Lookup > GPOS > Mark > Anchor-smallcaps. Then I use the "Create Accented Glyphs" command, but only some .sc marks are recognized. Others—such as circumflexcmb.sc—are not, and FF defaults to the standard .comb instead of the comb.sc version: https://ibb.co/VYdMzzJz Yet, the correct accented glyph apparently appears in the lookup: https://ibb.co/LbyTMSQ Is this a bug (or am I making a mistake, even though my procedure is consistent)?