When trying to move a draft post to a new date (typically in the future as I have many drafts that are in the past that I never got around to scheduling in) I always (never seen it work right) get the red pop up that 'Looks like someone else already moved this post.' error.
The thing is that I'm the only one logged in, and no one else has moved these posts, or is trying to move them at the same time. I've tried it with multiple draft posts.
Same issue in both Chrome and in Firefox. I ran the test at the bottom of the calendar page in both, this was the result
Not sure what to trouble shoot next.... :)