Can't drag'n'drop to desktop in KDE

Assuming this is a KDE issue:
I have a file on my desktop, setup so I can drag’n’drop onto it, and it will ask for authorisation, and run it as root. This has previously worked fine, but has broken (recently?), such that if I try and drop something, it will just copy/link it to my desktop folder. This is still working fine if I try and do it from one Dolphin window to another. (ie if I drag the /etc directory from one window, across to another window, and drop it on my link, it will ask for authorisation, then open in a new dolphin window, with full root permissions.)
Why will KDE not allow me to drop it?

Which KDE?

Whatever comes with Leap42.1…
As per sig, 5.5.5??
Is there another description? Thought by going to Configure Desktop/Help/About KDE, there should be a version there, but no…?