It seems as if sweeper emits a wrong dbus signal:

- LANG=C strace -o LOG -s 4096 -e sendmsg sweeper
sendmsg(8, {msg_name(0)=NULL, msg_iov(2)=[{"l\4\1\1\0\0\0\0\34\0\0\0a\0\0\0\1\1o\0\25\0\0\0/kickoff/RecentAppDoc\0\0\0\2\1s\0\16\0\0\0org.kde.plasma\0\0\3\1s\0 \0\0\0cleanRecentDocumentsAndDocuments\0\0\0\0\0\0\0\0", 120}, {"", 0}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = 120

- LANG=C dbus-monitor "interface=org.kde.plasma"
signal sender=:1.77 -> dest=(null destination) serial=27 path=/kickoff/RecentAppDoc; interface=org.kde.plasma; member=cleanRecentDocumentsAndDocuments

The signal "cleanRecentDocumentsAndDocuments" does not exist anymore. I think it should be "clearRecentDocumentsAndApplications":

- qdbus org.kde.plasma-desktop /kickoff/RecentAppDoc
signal void org.kde.kickoff.recent.clearRecentDocumentsAndApplications()