I expected to go into my furnace, but instead, it wouldn't open. I had things in all of my hotbar, except one spot. Clicking it with an empty hand seemed to open it. I saved and exited, then came back, everything was running fine.

Steps to Reproduce:
1. So the first thing I did was ride a horse, the saddle was on, including the iron armor.
2. I got off, I put a lead on it, lead it outside, then went on it again.
3. Got off, went indoors to check a furnace, and that happened. It was also raining, if that helps.