All changes in the "Bug Fixes" section of 5.5 of Lucene have been backported to 5.4.1 but https://issues.apache.org/jira/browse/LUCENE-2229 (thanks Mike for the help). The reason is that it changes the behaviour of the highlighter and I'm afraid that some users might be relying on or expecting this bug, so I'd rather fold it into a minor release than a bugfix release.
I'm not really qualified to know if there are things worth backporting on the Solr side, so if you feel like some issues should be backported for this bugfix release, feel free to go ahead.
