Oh that reminds me of something I keep forgetting...
When you zoom your game layers with ScrollX/ScrollY Rate 0 won't be displayed correctly anymore. With earlier versions of Construct it still worked properly.
Excuse me if this problem was already stated somewhere else.
Is the scroll rate set to 0%, and is the scroll X, Y position to 100%?
I had this problem once, but that seems to have done the trick...