Here is something hard to understand, but if you take a look at the demo which gathers all the most common use cases, it makes sense.
As potential use cases, we have:
- I want to access a protected page using Facebook
- I want to authenticate with Facebook and will stay on the same anonymous page
- I want to access a protected page using Twitter
- I want to authenticate with Twitter and will stay on the same anonymous page.

For Twitter, you can cancel the authentication during the process (there is a button for that) and in that case, you are redirected back to the application without any specific information for authentication.
And thus you have two cases: you were trying to access a protected page or you are staying on an anonymous page and we don't have the same behaviour in both cases, that's why using only one authorizer (not aware whether the target page is protected or not) doesn't wok. I don't use it anymore as it's already handled by pac4j...

The flow is always to redirect to the saved url...