Weird RSpec model failure during my Rails 4 upgrade. Ideas?

gistfile1.txt

def process!
  self.transaction do
    foo
    bar
    baz
    boom
  end
end

foo creates and populates part of obja (of class Content) and obja.save!
bar does obja.build_objb and objb.save!
baz updates more obja attributes and obja.save!
boom updates more obja attributes, and obja.save! fails on a validation error

And the failing spec...

    it "does not create new Content" do
      expect { request.process! }.to_not change(Content, :count)
    end

wtf.

Oh, and this is Postgres... could it be some kind of nested transaction problem?