The font eclass (font.eclass) runs "fc-cache -fs" twice, first in postinst and then in postrm. This seems like a bit of a waste to me. Reproducible: Always
needs to be run on install of new font: postinst. needs to be run on uninstall of a font: postrm. needs to be run on upgrade: postrm. but there's no way to know that we could have skipped postinst until postrm is run.
forgot. needs to be run on reinstall: postinst so really no way of knowing.