If the server is placed under extreme load, this will eventually happen.
https://www.youtube.com/watch?v=jUxaE6sjpRM
One of the clients will not recieve terrain data, and neither client will update their items. then the items get stuck in a perpetual fall loop.
Related issues
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This is a client sided (unmodded) issue. The items appear in a different places for each client

That's MC-4
No, it's not. Even if the player moves away from the falling stack of items according to the server, or even just stops dropping them, the items will continue this is a loop until the clients reconnect. Also, this is not a server-sided issue (after things have broken), as reconnecting shows the items clumped up where they were "dropped."

Just check the video a little more closely, and yes, the server is modded => Invalid
Also, the latest version is 1.8.1, so your ticket is also not up-to-date.
I just told you, galaxy, it is CLIENT SIDED.
The team on these forums/wwhatever also waited until now to fix the issue; it was created before 1.8 was released.. I know the server's modded. I developed the darn thing!
Good on ya
I will try to reproduce this in 1.8.1
Invalid because server is most likely modded.