Having played during the easter event and had 3x eggs from adventures with the bonus, I had expected to be getting 3x pumpkin refills with the bonus from halloween event. Also the dev diary says: 'The seasonal adventures are back again, with the same feature: the bonus applies to resources, including refillers, but not to the XP obtained, nor to the buffs or buildings.'
After playing The Siege a number of times and also a couple of Surprise Attack, I have found that the bonus is working for resources but not being applied to pumpkin refills.
This doesn't seem the correct behaviour to me.
Thanks