Martijn brought this to my attention, and I committed a fix + test to trunk.
But via IRC:
[16:46] <yonik_> mvg: is there anything in a released version of Lucene/Solr that uses SentinelIntSet in a way that causes it to resize?
[16:47] <yonik_> if not, no CHANGES entry needed...
[16:48] <mvg> Yes in the TermAllGroupsCollector and in some impl of TermAllGroupHeadsCollector
[16:49] <mvg> Both collectors can take an initial size.
[16:49] <mvg> The SentinelIntSet can grow in these collectors.
The default on those collectors is 128, so most likely no one was bit (i.e. they would need to override that default), but we should add a CHANGES entry and backport to 3x.