This is a problem that happens pretty frequently and has had some pretty terrible results. When one player throws out or recalls a pokemon from a slot (as an example, the third slot in your part), it sometimes causes another player on the server in that same slot to throw out or retrieve that pokemon as well, whether they are in a battle, flying, or anything else. This has caused people who are using that slot for their flying pokemon to sudden fall out of the sky to their death. Though a little rarer, when someone uses an item or Pokeball in battle, sometimes another player will get a message stating 'You do not have this item.'

After some testing, it appears that when someone presses 'R' when they have that slot selected and it does nothing, it is apparently getting crossed with another player and tossing their pokemon out inside.