Yeah, I definitely wasn't happy about it.Oh my gosh, I think I probably would have either screamed or cried.
I had just finished filling the space below the tree and was in the process of collecting everything that dropped. When I went to pick up the acorn, I got the "bag is full" message and thought to myself "awesome! I must have a full stack!" So I trot off to dump my stuff in that box outside Nook's. After grabbing the acorn that I couldn't pick up before, I went to craft a leaf pile and I couldn't because I had... 1 acorn. I think while I was emptying my inventory I must have just mindlessly clicked anything that was remotely brown. Clearly not my brightest moment.