It's not a bug, it's a feature. Downvotes mean "I want to see less like this." If a person generates content that other members want to see more of, they quickly reach a point where they are allowed to post it at a rate only limited by how quickly they can generate it. Why limit someone's productivity if their work is getting a positive reception? But if their contributions attract mostly negative attention, it makes sense to limit their activity on the board until they improve their conduct to the point where their contributions are more welcome.