Apologies if I've missed something (like maybe this is an ubuntu patch on top of COTS GNOME). list not cc'd to avoid my embarrasment if I have :-)
Try unchecking the expand option.. this only applies to non-expanded panels.
What is the general opinion on having the panels automatically lock to the side of the screen? makes it impossible to put a panel near the edge.
I think I will write a patch for this soon, but I would love to get as much input as possible first. Thanks.