They are simply clones of KDE Partition Manager's icon which is super weird and confusing. If we want to theme 3rd-party apps, we need to be respectful of their branding, not obliterate it in favor of our own.
Even with this commit, Partition Manager still suffers from this issue, but that's because it doesn't have its own icon yet. We'll fix that, then fix this issue for Partition Manager too. For that, see system/partitionmanager#7 (closed).
BUG: 467319 FIXED-IN: 5.105