Inability to expose province filter

I'm hoping someone can decipher this for me. I'm in the process of upgrading a site from D6 to D7. Exposed province filters in the old views no longer work. In creating new views, a country filter works fine but when I try to create a province filter, it doesn't even give me the option to expose it -- instead I get the error message copied below.

I tried testing the issue by limiting the public function operator_options on line 99 of the location_handler_filter_location_province.inc to just the one is/is not option. That resolves the issue -- it lets me add an exposed filter to the new view, and the filter works correctly. But it's obviously not a permanent solution. It is, however, the only one I've found so far -- I've tried everything else I can think of.

Any ideas?

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /admin/structure/views/ajax/config-item/new_user_registrations/page_3/filter/province
StatusText: OK
ResponseText:
Notice: Undefined index: single in /home/family/www/drupal7/sites/all/modules/location/handlers/location_handler_filter_location_province.inc on line 99
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