Laravel 5 Session ID regenerates on every request

I have a bit of a problem with the laravel sessions. When I apply the 'web' middleware to a route group, the session ID for the user that visits a page in that group gets refreshed on every request. The session itself works just fine and values are persisted. But the session storage gets flooded with session data. I tried it with local PHP, in homestead and on Forge. All yield the same result. At first I thought it was a problem with my application, but a fresh install of Laravel has the same issue. The code below is enough to reproduce the issue. Or is this intended behavior?

Route::group(['middleware' => 'web'], function() {
    Route::get("/", function() {
        return "hi";
    });
});