I was working in my Redstone testing world (it is a creative super flat world for testing my designs and making sure tutorials work before I build them in survival) and a trader llama had gotten in my way. I have DoMobSpawning set to true as there is a hostile mob farm built in this world. I went ahead and killed it, and didn't bother with getting the sword out of my inventory. I later tried breaking a block with it and it was impossible. There wasn't even a breaking animation either, it was like breaking a block in adventure mode. I tried it a few different times making sure that I was in creative mode, and the issue was consistent throughout.
Everything else seems to break just fine, making this issue even more peculiar. While it isn't a major issue at all, I wanted to make sure it was addressed.