To produce this bug follow this steps.
1. Open the inventory menu in creative.
2. select any mod spawner, and put in your inventory.
3. select any block or mod spawner again, and put in your inventory.
4. move your mouse pointer in the first spawner you choose.
5. then press the number of your keyboard to change the item to your selected block or spawner.
6. the exit the inventory menu.
7. press you keyboard to the mob spawner item you first choose.
8. then summon it.
This is what will happer.
when you spawn you selected mob spawner the spawner do not your mob, it will spawn the selected block or mob spawner you choose HOPE YOU UNDERSTAND if you don't understand much please contact me or email THANKS.