My posts unpublish when editing

I think I’m experiencing a bug. When I publish my work it’s fine, but sometimes I’ll go back and edit it only to find out that it has unpublished the post. This is very annoying because sometimes I don’t notice it right away until I see the link is now broken. Today it seemed to happen just by viewing an old post in the admin. Any ideas, I’ve been using wordpress for 2 years now and this has only recently started to happen?