I don't believe I was. Let's see... No, it was the forge not the anvil. I tested it. Here's what I did. First, I dropped a scarf on it, no crash. Next, I built a new web whip, put that on it. Nothing. deforged piece of iron, put it on it. Nothing. Picked up a web whip, clicked it on the forge then on a bottle. Crash.
Wasn't sure what did it so went to recreate it. Took awhile but I'm certain now. The crash happens when you attempt to click while the text cannot use this item there is up and then an item is place on top of another item. This seems to usually happen if you try to put an item that can't be deconstructed in the forge, but I've had the text pop up at other times when moving items around.