currently expanding and collapsing palettes causes them to pop around, can they be anchored so that they expand to the left and the right most palette remains as an anchor?
this may not be the solution but there seems to be something not quite right about the current behavior.
Yeah there's been something "not quite right" in the last two versions of Photoshop with the Panel docking and interface. The panels are absurdly easy to drag out of place. This has got even worse in CS5. If you are using a Wacom, unless you are extremely careful, they just pop about all over the place. CS2 and CS3 had much better, if less visually appealing, interfaces in this respect.
it's actually quite funny when you consider that the current behavior of collapsing a palette frees up space to the right of the palette!
if the right palette is "locked" to the edge of the display the collapsing does move right, the problem is that if it isn't squeezed up against the edge of the display it jumps to the left. Make the collapsing palette direction consistently to the right.