I was wondering why ProBoards has been doing that. I have had it in several of my posts. It's nothing I am doing (I don't think...) and is just added automatically.
I saw somebody say it had to do with pinterest links, but I swear I've seen it in posts without anything like that.
It's capturing pinterest code - if you remember for a while sometimes ppl's posts would have random pinterest urls at the bottom, now that's been replaced with the "Save". It's the pinterest code that somehow is getting caught up in ppl's posts. See the picture? It's the little button.