Just discovered that all the groups I belong to have suddenly got a new feature 'seen by'. All the posts I've looked at in the past have me logged as having read these posts.
I'm not too overly concerned about other group members knowing I've read their posts. However this new feature came in without any warning that I noticed, is retrospective and frankly I don't trust facebook not to make it for the entire site and retrospective.
I've messaged facebook but have not yet heard back. Does anyone know anything more? I think after this and the recent issues about private messages being visible on timelines I'm going to cancel my facebook account.