I think I may have figured it out -- I was editing in a recipe view, rather than in a brew session view. Didn't get the error when I switched to a snapshot brew session. I'm guessing that the software initially choked on the fact that it couldn't add inventory items to a recipe that was already...

Okay, this is a new one for me. I just started using the inventory feature, so I suspect it has something to do with how I used it, but has anyone seen this error before? Also, I didn't notice this error the first couple of days that I had the editor open.