I was showing off a VL box to an interested party. I introduced and demonstrated the command "htop" as the Linux equivalent to Task Manager. I may have moved the cursor down the list with the arrow keys. I closed the terminal window by clicking the "X" in the upper right corner. Result: all the desktop icons disappeared. I right-clicked the desktop space and the desktop turned completely black except for the task bar at the bottom.
To recover the desktop, I reconfigured Xorg via VASM from TUI. Negative results. Finally, I opened Display settings on the black desktop and "Allow Xfce to control the Desktop" was de-selected in that dialog. Re-checking this option recovered the desktop and icons.