Cannot Send Bulk Email via List of Event Attendees

The critical bug here is that I am unable to send a bulk email to people who have registered for an event (it may be a problem for other bulk mailings - say from a search - but I haven't tested that).

To reproduce the bug:

1. Via civiEvent, list the participants of an event
(e.g: http://joomla.demo.civicrm.org/administrator/index2.php?option=com_civicrm&task=civicrm/event/search&reset=1&force=1&event=1&status=true)

2. Select "All XX Records", choose "Send email to contacts" from the dropdown list and click "Go"
(URL: http://joomla.demo.civicrm.org/administrator/index2.php?option=com_civicrm&task=civicrm/event/search&&_qf_Email_display=true&qfKey=3e54dde3d7315b385a28290b04f6e2f7)

3. Fill out the email details (Mailing subject and text message), then click "send email".

4. You'll see the error message below:

Sorry. A non-recoverable error has occurred.
HTML_QuickForm_Controller: Unhandled action "upload" in page "Email"

Error Details:

Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] =>
[message] => HTML_QuickForm_Controller: Unhandled action "upload" in page "Email"
[mode] => 16
[debug_info] =>
[type] => PEAR_Error
[user_info] =>
[to_string] => [pear_error: message="HTML_QuickForm_Controller: Unhandled action "upload" in page "Email"" code=0 mode=callback callback=CRM_Core_Error::handle prefix="" info=""]
)