To reproduce: 1. Start Okular from a terminal. 2. Click Help/About Okular (get several messages saying "Trying to load Attica plugin:" and lastly "Using Attica with KDE support" 3. Click Close in the About box. 30 messages are displayed: okular(507) KWidgetItemDelegateEventListener::eventFilter: User of KWidgetItemDelegate should not delete widgets created by createItemWidgets!
kdelibs thing
The "Trying to load Attica plugin:" and "Using Attica with KDE support" are part of attica which is not kdelibs either, was fixed in https://projects.kde.org/projects/kdesupport/attica/repository/revisions/2dc59c06b87610e4bd9a07716435f0f80756f5e2 not sure when it'll make it into a release though
I'm working on the "KWidgetItemDelegateEventListener::eventFilter: User of KWidgetItemDelegate should not delete widgets created by createItemWidgets!" one
Fix posted for review at https://git.reviewboard.kde.org/r/105627/
KWidgetItemDelegateEventListener issue fixed in 9aaa24814030041f51405182f03c9760e04bc76f