Duplicate submit button id makes ajax fail in certain circumstances

I've been battling with an issue where where the poll form (as a block) would fail to submit via ajax when placed in certain positions on the page. Eventually I found that within Drupal.settings.ajax the key for the ajax element was 'edit-submit', but the id of the submit button had changed to something like edit-submit--3, presumably to prevent an id clash with another form element.

It seems that specifying a unique id within advpoll_choice_form() fixes this issue. I have attached a patch of one possible solution.