Steps to reproduce bug:

1) create plugin

2) have an item frame in the world

3) put an item in the item frame

4) schedule a repeating task to change the rotation of the item in the frame every 300ms

// example:
	public void rotateItem() {
		if(this.linkedFrame.getItem() == null)
			return;
		
		this.linkedFrame.setRotation(nextRotation());
	}

	private Rotation nextRotation()
	{
		
		currentRot ++;
		if(currentRot >= Rotation.values().length)
			currentRot = 0;
		
		return Rotation.values()[currentRot];
		
	}

5) start server

6) log in to server

7) item will be rotating every 300 ms

8) leave server and rejoin

9) item ceases to rotate.

I can not get the item to rotate again without restarting the server or doing a /reload

changing worlds, going far away until the chunk unloads does not fix it nor does dying.