window.onblur trying to set properties after object is destroyed

[victorssilva]

When running ember test --server and clicking in and out of the browser we spawn, we get multiple of these:

Uncaught Error: Assertion Failed: calling set on destroyed object at http://localhost:7357/assets/vendor.js, line 12972

window.onblur and window.onfocus seem to still try to set properties on destroyed objects.