While adding the Polish kreska as described in the blog post:
I ran across an issue when using diacritic-glyph-name.case for capital letters and Reset Anchors (Option-Command-U). Reset anchors does the right thing in the mark glyph with an ending of .case. So, acute.loclPLK.case would work. But, when named acute.case.loclPLK, Glyphs assumes it’s for lowercase, placing the anchor at the x-height.
But, to add a glyph like Cacute.loclPLK, Glyphs wants acute.case.loclPLK to combine those components. If the mark is named acute.loclPLK.case, then the Cacute.loclPLK glyph is added incorrectly using the acute.case component.
Hope that makes sense. Let me know if you need further details or a better explanation.