Hello,
I have a couple scenes where I scale up some WorldSpaceCanvas instances with some simple UI. I recently took the latest preview release and noticed that children are offset strangely until the canvas reaches its full scale. I made a PG which should demonstrate what I am talking about:
http://www.babylonjs-playground.com/#W9SZY#2
It's most obvious with the title, but it happens with anything which isn't very close to 0,0, it seems.
Thanks for a great framework!