Weird behavior of facter in a custom fact

gistfile1.txt

[root@ops-jenkins01-use1 facter]# facter --puppet operatingsystemrelease
6.3
[root@ops-jenkins01-use1 facter]# facter --puppet operatingsystem
CentOS
[root@ops-jenkins01-use1 facter]# facter --puppet operatingsystemmajor
2.6.32-279.5.2.el6.x86_64
[root@ops-jenkins01-use1 facter]# cat operatingsystemmajor.rb 
#
# Custom fact to:
#  return the major release number of the client OS
#  allow AWS instances based upon the Amazon AMIs to return a sane value
#
#
Facter.add('operatingsystemmajor') do
  has_weight 50
  setcode do
    if Facter.value('operatingsystem') == 'Amazon'
      %x[cat /etc/system-release | awk \{'print $5'\}].chomp
    else
      f = Facter.value('operatingsystemrelease')
      u = f.split('.')
      f
    end
  end
end