If a player left-clicks the air while a hidden player is standing in front of them, I expect PlayerInteractEvent to be fired with Action.LEFT_CLICK_AIR. Instead, no PlayerInteractEvent event handlers are invoked.
I assume that while the Minecraft client thinks that the player is hitting air, Spigot thinks that the player is hitting the hidden player, and is not firing the event.
Here's a minimal plugin source that can be used to reproduce this issue:
To reproduce, log in with 2 accounts to a server running this plugin. Have one player stand somewhere identifiable, like on a tower of blocks. Have the other player punch the air where the other player should be standing, and notice how the broadcast message is not displayed in the chat.
I'm unfamiliar with CraftBukkit's source code so I'm not sure if there's more to it, but FWIW I was able to resolve this locally by changing line 1196 of PlayerConnection.patch to this: