good demo of my problem: http://fabricjs.com/hovering If you select any item, it is displayed on top. In earlier versions (1.5.0 - 1.6.2) this problem does not exist. Sorry
If you dont want thie behaviour, you can set the preserveObjectStacking to true. Check the docs here: http://fabricjs.com/docs/fabric.Canvas.html
However, there is this one issue with background objects, so beware https://github.com/kangax/fabric.js/issues/3095
Hopefully, they'll push a fix soon otherwise your last resort would be going back to 1.6.2.