Mobs are not dropping equipment they have.

I was making a bunch of command block things, because that's what I'm in to lately, when I tried making a Leprechaun. I spawned it in and noticed it wasn't dropping its carrot on a stick. So, I then set it to 100% drop chance. Still no drop. After, I attempted a few more times, just the plain zombie drops. So, I tried a mob that previously dropped items, and the same thing happened. Then I tried another world, same thing.

How to Reproduce Issue
1) Give yourself a command block (/give @p command_block)
2) Paste in this command /summon zombie ~ ~1 ~ {HandItems:[{id:diamond_sword,Count:1b},{}],HandDropChances:[1.0F,1.0F]}
4) Kill the zombie