IntegrityError: duplicate key value violates unique constraint "ticket_change_pk"

[Ryan J Ollos]

While editing a comment on trac-hacks.org yesterday I saw this error. It might have been due to a double-submit, but didn't we already fix that issue in #10138? I'll have to refresh my memory on that.

2015-12-02 17:07:48,264 Trac[main] ERROR: Internal Server Error: <RequestWithSession "POST '/ticket/12588'">, referrer 'https://trac-hacks.org/ticket/12588?cnum_edit=8'
Traceback (most recent call last):
  File "build/bdist.linux-i686/egg/trac/web/main.py", line 554, in _dispatch_request
    dispatcher.dispatch(req)
  File "build/bdist.linux-i686/egg/trac/web/main.py", line 247, in dispatch
    resp = chosen_handler.process_request(req)
  File "build/bdist.linux-i686/egg/trac/ticket/web_ui.py", line 182, in process_request
    return self._process_ticket_request(req)
  File "build/bdist.linux-i686/egg/trac/ticket/web_ui.py", line 578, in _process_ticket_request
    ticket.modify_comment(change['date'], req.authname, comment)
  File "build/bdist.linux-i686/egg/trac/ticket/model.py", line 560, in modify_comment
    old_comment or '', str(when_ts)))
  File "build/bdist.linux-i686/egg/trac/db/util.py", line 128, in execute
    cursor.execute(query, params if params is not None else [])
  File "build/bdist.linux-i686/egg/trac/db/util.py", line 72, in execute
    return self.cursor.execute(sql_escape_percent(sql), args)
IntegrityError: duplicate key value violates unique constraint "ticket_change_pk"
IntegrityError: duplicate key value violates unique constraint "ticket_change_pk"