It's an Elasticsearch bug, or more precisely a bug in Joda-time.

I could reproduce the bug with version 2.9.4 (the version used in ES 2.4.1, which is also the last release at this time), but not with the current master (https://github.com/yrodiere/joda-time/commit/e6dd4ba04d1e16bbc9c98cfd19f330a15b6fd060). I think the fix is here: https://github.com/yrodiere/joda-time/commit/eaaff1d0687fc86a745ca8f3ea0b069b3cf54233

I reported the bug to the Elasticsearch team, they probably can fix it by upgrading Joda on their next release (provided Joda releases the fix before then): https://github.com/elastic/elasticsearch/issues/20911