In addition to crashes when editing system palette values reported elsewhere...
I cannot create a new palette from the current open document. I have a three page pdf with simple colour bars on each. Nothing else. Create Palette from Document > system palette... results in colours from currently selected page only!
Next, copied all bars to one page, tried again. Better, but not all colours were captured!!
So - all in all I cannot create a custom palette at all. Boo.