Yes, same here.. maybe the Preview saved with these Folder visible..
No Problem you can hide these Folders.. use Terminal.app
sudo (if you want to do this as Administrator)
type "chflags hidden" (drag and drop the desired Folder here opt, mnt, sw...), without the qoutes, press Enter
if you use the sudo-command you have to type in your password.
in Finder you see disappeard the dropped Folder.
to make it visible, use nohidden instead of hidden.
Hi, if this was useful for you, it would be nice to get a feedback here,...