This is related to SGSK + NGUI + TNet package, updated to NGUI v3.6.8 (works fine)
I followed your video instructions to setup my Unity layout to match (thank you BTW).
If I drag an NGUI prefab and drop it onto the hierarchy; it seems to work as expected (the control works). However, if I drag either from the NGUI toolbar OR the actual prefab and try and drop it onto my selected panel in the SCENE view; I get many, many spawns of a new UIRoot (it creates several per second while dragging the object in the scene view.
It also messes up my 2D camera and resets the mask which then makes the whole thing buggered up

There is probably something with the existing layout even though there already IS a UIRoot; I'm hoping you can resolve it fairly easily.
Screenshot for words +=1000;
Edit: v3.6.9 will resolve this issue