Form automatically disabled?

I got a report from a user that an application form installed on my site at had gone away. Sure enough, it was gone. At the back end I discovered that the form was ‘disabled’. I enabled it and it’s back. The form has been live for several weeks with about 400 submissions, including 12 this morning. Somehow this afternoon while I was away from my desk, the setting went to disabled. I’m the only admin. Any ideas how this could happen?