Different behavior when type=list in add_argument [Breaking Change]

[sibelius]

I've noticed that when you don't set a location and have a argument with type list, the behavior os parsing them is different than when I set up the location='json'

Example:

parse = reqparse.RequestParser()
parse.add_argument('arg1', type=list)
parse.add_argument('arg2', type=list, location='json')
args = parse.parse_args()

When a have a POST using the Content-Type = application/json like this:

{"arg1": [{"id": "123", "name": "testing"}], "arg2": [{"id": "123", "name": "testing"}]}

I have this result:

args['arg1'] equals ["id", "name"]
args['arg2'] equals [{"id": "123", "name": "testing"}]

[sibelius]

This wasn't happening on Flask-RESTful 0.2.12

[sibelius]

this should be consider a breaking change if the behavior doesn't work like before

[joshfriend]

This is probably related to #380. I was unable to find a good solution for this and the PR I did submit to Werkzeug was declined. Due to #335 I don't feel that it is worth the effort to chase this down further.