Intel has released a beta version of a new BIOS firmware for Haswell NUCs. If you're feeling adventurous, download the latest BIOS from Intel's Download Center. This works only on Haswell models (D34010WYK and D54250WYK), so don't try to do this if you run a Bay Trail or Ivy Bridge NUC.
According to Intel, this BIOS version will resolve a shutdown problem in Linux installations. Some user reports confirm that it's not any more necessary to disable the Wake On LAN feature to make the shutdown/suspend work normally.