How to recreate:

1.Set-up a beacon,
2.put an item in it,
3.exit the beacon menu without clicking done, (before MC-64490 gets fixed, selecting done will also work),
4.break the beacon,

What happens: only the beacon is dropped and the item in it is lost
What should happen: beacon and the unused item in it should both drop

I assume that this is not intended so I reported it as a bug.