KDE Frameworks 5.111 available in Kubuntu Backports

[Snowhog]

But the question remains: how could this happen?'
You certainly didn't create /etc/apt/sources.list.d/kubuntu-ppa-ubuntu-backports-mantic.list manually and forgot to add the "deb" line…

No, I didn't. I'm sure, that 'some time back', I edited those two sources and removed the wrong line. As a rule, I don't keep the deb-src sources entries, as I don't build from source. Just a stupid mistake, and explains why I wasn't able to "see" it staring me in the face!