Disappearing pollen stain?

I had a hand made canvas feeling (there was no specific material listed) and I left it under some flowers I had on the table. When I woke up the next morning, there was pollen on the outside/inside of the bag! Having a moment, I wet a rag and attempted to wipe the pollen off. No surprise it left a stain! Busy with work/school/life, I never got around to even thinking about washing it until about a week after the wet rag incident. No one else had the chance to wash it, since it was in my keeping the entire time. Curious enough, when I went to go wash it, I couldn't even find a trace of the stain! Can anyone explain why this happened?