slots in inventory freeze inventory when moused over.

When I mouse over some slots in my inventory to move items in or out of my inventory, the inventory freezes for the duration of my mouse hovering over those slots. other slots in the inventory work fine.

Usually:
I can move things around my inventory without freezing or other issues.

For some odd reason this happened:
I opened my inventory to move things from my tool bar to the top of my inventory, and found I could not place anything in the farthest right top corner. whenever I mouse over it, it would freeze for until I moved the mouse off of that slot. It happened with a couple other slots but I did not memorize where they were.

Steps to Reproduce (this is happened before the bug suddenly appeared):
1. I walked into a nether portal to explore the nether for the first time in the snapshot.
2. I dismantled a tree and opened my inventory to look at the new items.
3. Then I closed my inventory.
4. I picked up more things.
5. I opened my inventory, to sort items.
6. I got confused about the bug because it just happened.
7. I experimented to see if I could fix the bug by leaving and returning to my inventory.
8. Basic things IT didnt seem to fix the bug so I came to report it.

• Basic IT being: 

• • Restarting the minecraft world

  • entering and leaving inventory

  • checking some ghost item wasn't there by using rightclick and drag to put a torch in the broken slot (somehow that didn't freeze)

9. I clicked F11 to window minecraft and I started making this report.

10. I looked back at minecraft for a moment because mobs were attacking.
11. The bug had somehow automatically resolved itself.
12. I believe I fixed it by accident by windowing minecraft with F11.