I write completely custom proposals, so I use the Ad-hoc line item many times while building out my agreements. Out of habit, when I mistype something, I press CMD+Z, but if this is done while editing a line item, it refreshes the page and erases any data you've entered since your last manual save. I don't mind if CMD+Z can't be used to undo typing, but gosh, I really wish it didn't delete the last 15 minutes of my work either.