This bug was discovered by accident, hoppers apparently can insert any items into the beacon block- which shouldn't be intended at all.
Not only the items can be inserted into the beacon block via hoppers, it will accept ANY items as fuel. Only certain ores were intended for beacon fuel. I'm pretty sure this is a exploit though.

Steps to reproduce:
1: Create a regular beacon pyramid
2: Shift-click to put a hopper next to the beacon, then insert any item into the hopper.
3: Choose a beacon effect and click done, the beacon will accept the item regardless if it's a ore or not.