copy/paste clipboard broken

After upgrading to Kubuntu 19.10 and KDE from kubuntu-ppa/backports, copy/paste is annoyingly unreliable.

After highlighting text and pressing ctrl+c, then pasting ctrl+v somewhere else, very often (70% cases? but not always) nothing happens.

This is because:
- highlighted text gets copied to the clipboard
- clipboard gets replaced with an empty string

The issue can be better seen on the attached screenshot.

It shows that:
- I've highlighted "Further information:" text, then pressed ctrl+c
- expanded Klipper shows "Further information:" on the second position, and "empty string" on the first position

As a result, ctrl+v does not paste anything; expected would be to paste "Further information:".

I've tried disabling klipper, but the issue remains.

The issue is similar to one described here:

https://www.reddit.com/r/kde/comments/b0hxoq/cant_paste_contents_from_clipboard/