I have seen charts end up in a user I named Review. I suspected it was user error since my AC uses the first name for messages/in boxes, and someone just didn't send it to the right "person". I wonder if AC uses the display name (first name) to check in box.
So my first response was going to be "user error""
Having said that I was playing around with this today. I was able to add multiple charts For my test patient without any warning (also strange, but not the purpose of my post)
I then sent one of those chart to another user,
And again was able to open yet another version of that chart without any warning.
Then I logged on as that other user. When opening a duplicate chart there I got the warning,
I deleted the charts that I had forwarded, and when I attempted to load the same patient chart after deleting, I got the warning chart was already in that users inbox when it wasn't.
That exercise certainly seemed to reproduce what you reported.
Then I tried the same thing all over again, and it all worked AS IT SHOULD meaning warnings were correct in the location of the chart!!
SO, it seems there is some strange behavior going on, AND WORSE it may be intermittent.