It introduces a change in behaviour on Solaris 11 systems. Before the change the old regex did not match, so sadly the following resolution was used as a (suboptimal) fallback value.

    Facter.add(:operatingsystemrelease) do
      setcode do Facter[:kernelrelease].value end
    end

If this change should therefore be targeted against facter 3.x i think we should remove the above rather pointless resolver in the same run (as discuessed in https://projects.puppetlabs.com/issues/11308)