json_object preset might not be encoded/decoded correctly

Haven't had a chance to try and debug this just yet, but I'm using json_object preset to validate json input for the mapview dataset extent field. The validation seems to work, but upon viewing the dataset read template I'm getting invalid json errors. When I go back to the dataset edit form, it's prepopulated by a python dictionary value (e.g {u'Polygon': []) etc..

No file or test is named. Start by reproducing the json_object preset with a mapview dataset extent, then trace the value from validation through the dataset read template and back to the edit form. Done means valid JSON renders without errors and the edit form round-trips JSON rather than a Python dictionary representation.

Written by the indexing model from the issue text.