Database Curiosity

Lately I’ve noticed something odd in my database. Every time I edit a post, it adds an “_encloseme” to that post ID in the database under postmeta. It does not do it if I edit a page. These never go away. I never saw this happen before a few weeks ago. It isn’t causing any problems with the actual blog right now but I’m wondering if it might later? Does anyone know why this is suddenly occurring?