When dragging a file icon on the KDE desktop in Folder View, the mouse cursor quickly alternates between the "Forbidden" cursor and the drag cursor. If I release the mouse button while it shows the Forbidden cursor, it ends up doing nothing. If I release the mouse button while it shows the drag cursor, the icon is moved as expected.
Unless I'm being careful, most of the time the cursor is the Forbidden cursor, which basically breaks moving desktop icons.
This doesn't affect KDE Neon, which has Qt 5.9, so it's likely a regression introduced in either 5.10 or 5.11.