Possible reason: There's a kleopatra.svg in breeze-icons/icons, but there's none in breeze-icons/icons-dark.

KIconTheme sets the fallback theme name to breeze, but those icons cannot be found because we only load the icon theme RCC for breeze-dark. I think we need to load both RCC files in dark mode. No, that doesn't work.

I think we need to add all breeze icons that have no equivalent in breeze-dark to breeze-dark before creating the breeze-icons-dark.rcc.

One more data point: breeze-icons installs a copy of all breeze icons that do not exist in breeze-dark in the breeze-dark icons folder. So, with icon files on disk breeze-dark has all icons that breeze has even without using breeze as fallback icon theme. Looks like an oversight that the breeze-dark RCC generated by breeze-icons doesn't include missing breeze icons.

And another note: In KF6 icon inverting happens automatically in ksvg or so, so that we don't need to ship breeze-dark anymore. And there will be a BreezeIcons library including the icons that can be used instead of the RCC file. This means we just need a quick fix for VSD and not a general solution for upstream.