Do you want to request a feature or report a bug?
Bug

What is the current behavior?
A React Component with an Event Handler (for example onClick) is rendered inside a Web Component. When the Component is clicked the Event does not receive the React Component (specified callback is not invoked)

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template: https://jsfiddle.net/reactjs/69z2wepo/).

You can reproduce it with Web Component example contained in the react repository (https://github.com/facebook/react/blob/master/examples/webcomponents/index.html): Replace the 'a' element with a button and add for example an onClick event handler.

You can find a modified version of the Web Component example (based on the 15.4.2 codebase - https://github.com/facebook/react/blob/v15.4.2/examples/webcomponents/index.html) here:
https://gist.github.com/nilshartmann/3a520920e5fc920bfde49e077ad3beab#file-index-html-L50

What is the expected behavior?
The event handler should be called.

For testing I have modified getEventTarget.js to return the target from the path property of the nativeEvent (instead of the "original" target from the nativeEvent). With this addition it works -
the Event Handler is called.

You can find the modified version also in the gist: https://gist.github.com/nilshartmann/3a520920e5fc920bfde49e077ad3beab#file-geteventtarget-js-L6

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
15.4.x and 16.x
I've tested in Chrome, Firefox and Safari. I don't know if it works in previous versions of React (don't think so)