knetattach (installed by default) has no icon itself, it is shipped in oxygen-icons which is loaded as default theme in the inheritance chain by kiconthemes (maybe latter should recommend it?) Reproducible: Always
In gitunstable oxygen has been removed from the inheritance chain http://commits.kde.org/kiconthemes/ad1ead84ee2c3a14363afdb048b3579f3d01fa18 and knetattach has been removed from the app menu
neon_01_nodisplay_knetattach.diff added to packaging to set NoDisplay=true