It was just a tweak to emoji characters to mark them all as East Asian Full Width instead of Narrow or Ambiguous so that they displayed correctly when using a fixed width font in a terminal console. This probably only matters if you like to use emoji filenames (you mad person), but it felt like a wart so I reported it & had a short back and forth with the chair of the emoji-related subcommittee which resulted in a proposal which was eventually accepted by the committee into Unicode 9.0. The committee were great: took my tiny bug report seriously, wrote huge long treatises to justify the change & eventually voted it into the standard.
(This was pretty much my peak geek achievement of 2016 so far :) )