On our alt run tonight, everyone who had completed the ring on their main was obtaining 13 runes per boss. I can't find anything on google, on the General forums, Bug forums, or MMO-C.
The latest round of hotfixes also mentioned nothing changing with Elemental Runes.
The exact way it would show up in our log was:
X has received Elemental Rune x9
X has received Elemental Rune x4
Previously, it was always only 9, or 27 if we procced the lucky streak. But never 13.
This drop rate was occurring on Heroic difficulty. It seems like they added some kind of +50% bonus to legendary component acquisition if you've completed this stage already.
There was not a +27 proc, so I'm unsure if we would have gotten +13, or continued to get +4.