Changing program from public to private or unlisted is not working!

If I write a program in the Online Editor (Public), is is visible to anyone. If i then change it in 'Title & Visibility' to 'private' or 'unlisted', it looks like the changes have been saved but still but everyone can see it. When I open it again, it is automatically reset to 'public'.
Can I delete that program, or is there a way to set it to private or unlisted?