I also confirm that temporal FIX by @shunsuke works.
I actually reviewed my project version control and noted that the PropertyReferenceDrawer.cs file only suffer that changed between a NGUI previous version I had before the update, so hopefully commenting that line will not break anything, it looks like no...
Hope to hear an official solution as it seems from reading forum post the latest NGUI version present a couple of issues in different areas.
Thanks guys for sharing the solution and reporting the problem!