### Version 2.4.2 ### Steps to reproduce Not actually sure what is causing the object to be observed (`__ob__` to be added); will try to create a minimal repro later. Update: Repro link: https://jsfiddle.net/49gptnad/508/  ### What is expected? For `__ob__` to not be considered an injection. ### What is actually happening?  As shown in the first screenshot, this seems to be happening because of the usage of `Reflect.ownKeys()`, which [apparently does `Object.getOwnPropertyNames(target).concat(Object.getOwnPropertySymbols(target))`](https://stackoverflow.com/questions/34449045/what-is-the-difference-between-reflect-ownkeysobj-and-object-keysobj), which is returning non-enumerable keys. <!-- generated by vue-issues. DO NOT REMOVE -->