Do you have plan to upgrade lucene libraries?
2. Also, a new method to analyzer is under tag 4.4.0-atlassian-03.
I have checked on the releases for 6.13.0, 6.10.2, 6.3.4, and 6.0.5 release it is not involved yet.
As I understand correct this commit will help
BTW, this commit can be affected for upgrade library in Confluence.
Also, major release was so long time ago: