Laravel 5 and weird bug: curly braces on back

Whenever I go back in history on my Laravel website, the response I see is this:

{}

When I go forward to where I was before that, it shows those braces as well.

The problem doesn't occur if I launch Developer Tools in Chrome with Disable Cache option. The Content-Type of what's returned is indeed application/json. In Firefox there's no such problem.

It happens because one of my Middlewares. I wrote AjaxJson middleware to translate all Ajax requests to JSON response. Weirdly, when I go back in history, Google Chrome makes this request Ajax. It contains this header:

X-Requested-With: XMLHttpRequest

And therefore $request->ajax() returns true.

This is my middleware:

<?php

namespace App\Http\Middleware;

use Closure;
use Illuminate\Http\Response;

class AjaxJson
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        $response = $next($request);

        if (!$request->ajax()) {
            return $response;
        }

        if (!$response instanceof Response) {
            return $response;
        }

        return response()->json($response->getOriginalContent(), $response->status());
    }
}

What am I doing wrong?

via Chebli Mohamed