[chaley]

This is interesting.

Calibre contains a dictionary "field_metadata" that contains descriptions of every field (column) in the library. It is supposed to contain only metadata, not values of the fields. Unfortunately the description of the field #kobolastread has had a value inserted, which is never supposed to happen. You can see this by looking at the field metadata section of metadata_db_prefs_backup.json.

I don't know how one goes about inserting a value into field_metadata. The only way I can find to do it is something like:

  fm = field_metadata.get('#kobolastread')
  fm['#value#'] = something

In this case 'something' is a JSON-encoded datetime value that looks like:

     {
        "__class__": "datetime.datetime", 
        "__value__": "2014-12-22T23:47:57+00:00"
      }

so perhaps the code looks like

  fm = field_metadata.get('kobolastread')
  json_encoded = JsonCodec().encode_book_metadata(book)
  fm['#value'#] = json_encoded['#kobolastread']['#value#']

Does the problem go away if you start calibre then connect CC without having connected your kobo?