Not sure if this is a bug or if I'm just stupid, but I'm banking on the latter. Move it to bugs if necessary...
I was trying to make a prism, so I built an alloying crucible. Clicking around like an idiot, I accidentally dropped a raw glass, and couldn't see it. So I moved the crucible to see it and pick it up. But when I tried to use the crucible after I set it down and got the glass, I discovered that I couldn't interact with it at all -- except to destroy.
I could have another one made within the hour with no real problem, but I'm really aggravated about this. Am I just not doing it right? Or is this a bug? Please help!