When attempting to move whole structures around on the screen, the structure snaps back to the original position.
This problem may occur when using a non-MacOS X native application under MacOS X via Classic mode. Restarting the computer may solve the problem. Booting in MacOS 9 instead of running in Classic Mode should also take care of the problem. The best solution is to upgrade to the latest version of ChemDraw. The latest version of ChemDraw is MacOS X native and does not have this problem.