Unable to use custom field as start_date and due_date

[anonymous]

Setting custom start_date and due_date doesn't work.

Setting example:

[ticketcalendar]
ticket.start_date = due_assign
ticket.start_date.format = %Y-%m-%d
ticket.due_date = due_close
ticket.due_date.format = %Y-%m-%d

After analyze source code, detect wrong parameters are passed to _to_date function in web_ui.py file.

125 def _to_date(self, d, format='%d/%m/%Y'):

After removing the self parameter, custom date started working.