I am having quite a bit of problem with jQuery as of Summer 16 updates. We have a developer edition and a normal dev sandbox and both behave very differently with the same browser with the same code.
Selecting an object with jQuery and logging it in the console on the dev sandbox gives this :
The exact same output on the Developer Edition goes like this :
So the first one seems to behave normally, and the code work as expected. I mostly use jQuery for DOM traversal as finding the closest TR, and then searching through classes of children and their siblings is much easier for me in jQuery than any mountain of vanilla JS code would do.