Rails Nokogiri XML parsing working locally, not on Heroku

I have the following script running in my rails app. When it runs locally, it parses all of the courses correctly (9673 results) but when I push it to Heroku, it returns exactly 2x this number (19346 results). Any ideas? Are there possible Heroku performance limitations that could be causing the cycle to repeat itself?

# Pulls all course data for specified year, based on subject list
subjectdoc= Nokogiri.XML(open("http://ift.tt/1xM0doJ"))
# Reads each subject and stores it in local variable prefix
subjectdoc.xpath("//subject/@subject").each do |prefix|
  # Link to course pages, substituting in prefix in URL
  classdoc= Nokogiri.XML(open("http://ift.tt/1BT5uBz"))
  # Reads each course and stores listed vars
  classdoc.xpath("/courses/course").each do |course|
    num = course["catalog_nbr"] || "Not provided"
    subj = course["subject"]    || "Not provided"
    title = (course.at("course_title/text()") || "Not provided").to_s
    cid = (course.at("sections/section/@class_number") || "Not provided").to_s
    inst = (course.at("sections/section/meeting/instructors/instructor/text()") || "Not provided").to_s
    # Creates a cornell class in Cornellclasses table
    Cornellclass.create(:prefix => subj, :coursenumber => num, :instructor => inst, :title => title, :courseid => cid)
  end
end