non-recoverable error when trying to update event address

This is happening on my installation but I have not been able to reproduce on test server.

The only relevant thing I can think of is that I have changed my address preferences after I created the event.

When I try and edit the address for the event I get the following error:

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

[code] => -3
[message] => QuickForm Error: nonexistent html element
[mode] => 16
[debug_info] => Element 'location[1][address][state_province_id]' does not exist in HTML_QuickForm::getElementValue()
[type] => HTML_QuickForm_Error
[user_info] => Element 'location[1][address][state_province_id]' does not exist in HTML_QuickForm::getElementValue()
[to_string] => [html_quickform_error: message="nonexistent html element" code=-3 mode=callback callback=CRM_Core_Error::handle prefix="QuickForm Error: " info="Element 'location[1][address][state_province_id]' does not exist in HTML_QuickForm::getElementValue()"]
)