Why does mongoid 3 randomly append '' to my association?

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class Question
  include Mongoid::Document
  has_and_belongs_to_many :tags, autosave: true # Refer to tag_ids
end

class Tag
  include Mongoid::Document
end

But every once in a while my data gets populated with:

question.tag_ids = ["", "", "brand", "descriptive", "mobile", "preferences", "technology"]

asked 1 min ago

Kamilski81

2,226