Created attachment 112063 [details]
Dolphin shown using Nautilus's icon
Kubuntu uses vanilla upstream AppData and .desktop files for Dolphin that specify its icon as `system-file-manager`: https://cgit.kde.org/dolphin.git/tree/src/org.kde.dolphin.desktop#n46
In all recent versions of Kubuntu (16.04 through 18.04), this somehow results in Dolphin displaying Nautilus's icon in Discover rather than its own; see attached screenshot depicting how it looks in Discover 5.12.4. I've spoken to the Kubuntu folks and they confirm that their Dolphin packaging is 100% vanilla for AppData and the .desktop file. It's not at all clear that they're doing anything wrong.
Could this be because the icon is named `system-file-manager` and maybe that conflicts with the same name used for Nautilus?
This is fixed in 5.13 by 7b3e6de68efaeefa9eb9cb2ffe0fa8c443091202.
What happens is that debian prefers gnome by default (and so does Ubuntu). When building appstream db, they don't default to Breeze like we do.
If you ask me, dolphin should install a dolphin.png/svg icon that it use itself, instead of relying on whatever theme is present.