SUMMARY
The drag-and-drop function for desktop icons is very unstable and hard to use; mouse cursor randomly flashes between the "banned" cursor and a standard dragging cursor during a drag.

STEPS TO REPRODUCE
1. Add a desktop icon.
2. Unlock widgets, unlock icon position.
3. Try to drag the icon to a new location.

OBSERVED RESULT
While dragging an icon to move it to a new location on the desktop, the cursor randomly flashes and changes between the "banned" cursor and a normal dragging cursor. Releasing the mouse button in the former situation cancels the icon position change. Releasing the mouse button in the latter situation completes the move.

EXPECTED RESULT
No "banned" cursor should ever be shown in this case. The possibility to move icons should not randomly change with mouse cursor movement.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: ArchLinux, kernel 4.19.12
KDE Plasma Version: 5.14.4
KDE Frameworks Version: 5.53.0
Qt Version: 5.12.0

ADDITIONAL INFORMATION
This is a Dell XPS 13, 4K, dual head with an external 4K monitor on the left side of the laptop display. This configuration may have some unexpected effects. (Otherwise I think that even very rudimentary testing would have revealed this obvious problem immediately.)