hello,
I am on 8.1. Occasionally it works for a while, when I am disabling and enabling plugins. But there is no consistent plugin causing an issue. I have spent two hours trying to find which one it could be. Also I have found that the upload bar doesn’t go green, even when it is working. It doesnt show a percentage upload or change from waiting status. Only once the Post Update button has been pressed, and it seems to be jammed, although sometimes it works, very occasionally. If the refresh button is pressed, then the status bar goes green, although no upload percentage happens. The page refreshes soon after that so it stops the post update. Most of the time, after waiting, the text is posted, but no image is found. I had the same issue when using twentytwelve theme for a test.
Thanks.