Date field with defaultFactory not saved

Sorry for the noise, I actually post this in https://github.com/plone/plone.app.dexterity/issues/203
I think it is a serious bug that need some attentions.

Steps to reproduce:

  1. Fresh install 4.3.7
  2. Create a simple Dexterity package with Date field and defaultFactory (see below).
  3. Install and add item under "Add new..." -> Book
  4. Add Title and save. (Note: no change in date field)
    The object Date field is None after save. This problem does not occur in Datetime field.
def startDefaultValue():
    print '---- startDefaultValue'
    return datetime.date.today()

class IBook(form.Schema, IImageScaleTraversable):
    """
    Book
    """
    start_date = schema.Date(
        title=_(u"Start date"),
        required=False,   #True also same problem
        defaultFactory=startDefaultValue,
    )

Thanks for finding that and filing the issue!