OS4 icons will not snapshot and they will eventually "disappear" if you mess with them too much -- if this happens, open a shell and delete the offending .info file. I've been converting OS4 icons to DualPNG format, which don't seem to have the same problem.
DualPNG icons have a couple of problems of their own. When used on a panel/dock, they display the selected image, rather than the normal image. DualPNG icons also don't release their selected state when you click on other windows, programs, etc. -- only when you select the desktop/window that they reside in or on. Def_icons also don't display their selected state (which I've mentioned before).