We've installed OG Vocabulary and tried to follow the setup instructions to the letter. We have five groups, each with one vocabulary, and one content type that has an OG Vocab Entity Reference field. It all works beautifully unless we attach a file to the content type. Then, at save, we're told that the OG Vocabulary term is required - for every group. The field is not required, which makes it all the more odd. Without an attachment, there is no problem.