resource.mkdir does not set metadata correctly

How to reproduce

1. Create S3-resource, specifiy default value for each obligatory field of the application profile.
2. Run

import coscine

token = "My Coscine API token"
client = coscine.ApiClient(token)
project = client.project("My Project")
resource = project.resource("My Resource")

form = resource.metadata_form()
form["Title"] = ["It would be great if you can see this"]

resource.mkdir("aa", form)

Expected result

Folder aa has the title It would be great if you can see this.

Actual result

Folder aa has the default title.