My guess is that you are able to zoom (change the scale of the layout) but the scaling doesn't happen at the point that you want, but rather from the center of the screen, thus offsetting your sprite and perhaps resetting your scale level..?
That is what my experience when I was fiddling with a similar concept, only it also involved parallaxed layers that were scaling from the 0,0 coordinates and not the current scrollx, scrolly position and it was a mess!
I just don't get how Constuct handles the 2Dish world when it comes to simple things like that. I wish there was a real camera system and world coordinates for positioning, scaling and depth perception.
Oh well, not only I wasn't helpful but I mumbled too much