Opening a sign-in pop-up doesn't return after successfully signing in

Opening a pop-up doesn't return after successfully signing in.

http://d2.naver.com/helloworld/6033708

Try logging in via Github in the comment section. A new pop-up will appear. Even if the login is successful at the new pop-up, the result is not being sent to the original <webview>.