In trying to arrange the panel to my satisfaction, I accidentally clicked on "Remove this Icons-only Task Manager. This hung the desktop. Cursor moving fine, but any clicks on anything on the desktop have no effect. Had to crash the session.
On trying to repeat it, to see how reproducible the effect was (it is!), something very odd happened. The task manager plonked itself on the desktop, obscuring some of the icons, rendering them unreachable. There appears no way to move it and removing it again hangs the desktop.
How to I get rid of the blasted thing? I attach a snaphot of the part of the screen, showing the empty task manager. The large Firefox icon underneath the white-ish square is also a part of the task manager display.