"Fix database writes for esoteric character sets, broken in the WordPress 4.1.2 security release"
In other words, despite the best efforts, expertise and experience of the Wordpress team, inevitably an automatic update to Wordpress broke some people's websites and the cure was worse than the illness it was meant to prevent. It's not surprising they want to keep this quiet and haven't publicised it like all the other core automatic updates.

All those calling for automatic updates to plugins should take note: If this can happen in the core, how much more will it happen in plugins.

All automatic update systems in Wordpress - be it core, plugin security updates published by the Wordpress team or any future plugin automatic updates - should have opt-out tick boxes within the USER INTERFACE (so any Wordpress owner can access it without needing technical knowledge) and make an informed decision for themself. Wordpress can put whatever warnings or disclaimers on it they like, so long all Wordpress users get a choice.