Sander Berkouwer (Directory Service MVP) wrote an interesting article about SID compression.

http://blogs.dirteam.com/blogs/sanderberkouwer/archive/2013/04/05/new-features-in-active-directory-domain-services-in-windows-server-2012-part-21-resource-sid-compression.aspx

Basically Microsoft  has identified some problems with new SID compression when connecting to NAS devices. If you face the problem SID comression can be disabled.

http://support.microsoft.com/kb/2774190