Comment 5 for bug 525368

The same happens to me with Lucid updated to now.

Maybe this helps debugging:

- When using two monitors, if you add a new panel to the right border of the screen that is on the left side, the panel is rendered on the left edge of the screen that is on the right side.

- In a single monitor setup, if you add a new panel to the bottom of the screen (in addition to the default one), the existing panel is moved up and a space for the new panel is allocated between it and the bottom of the screen. Very probably the new panel is then rendered below this space, out of the visible screen area.

So the "invisibility" reported is in fact the panel being rendered out of the screen.

Restarting X makes the panels visible in their correct positions.