I looked into this.
The thing is that spoilage time is stored in time, not percentage. So when the total spoilage time for pumpkin changes from 10 days to 20 days, they appear to have spoiled.
What's strange here is that the 20 day spoilage time for pumpkins is not being caused by having hallowed nights enabled in a world, but it is being caused by hallowed nights being the default event right now. This means that any world with any event setting currently has 20 day spoilage time on pumpkins instead of 10.