Q:
Why do my palette items seem to jump when I drop them onto the canvas?
A:
With grid placement of your symbols, you'll note that when grid is 'on' in a document, Diagram! places newly dropped symbols on that grid (places their upper left hand corner on a grid point).
The symbols on your palette, however, are not grid aligned -- individual points may originally have been aligned to the grid, but your group was not. Thus, when they're dropped into a new document, Diagram! repositions them to be grid aligned (places the symbol *group's* upper left corner on the grip, but not necessarily any of the original points).