Twice my Bishop Oil has disappeared out of my helper's pack

I put the oil, the heart, and the ingots on my helper for Nellie's quest. I logged in this morning and the oil was gone. So I went and got it again. And when I logged in a moment ago, checked her pack and it was in the first slot for 10 seconds. Then it was gone. She isnt marked to refuel items, I wasnt crafting, so where did it go?