"Forced login" setting interrupts Hierarchical Select callback

I remember having this problem before... When I had taxonomy relationships in a view, and some of the content displayed by that view didn't have at least 1 term attached to it from the vocabularies involved in the query, I got exactly the same problem.

In the end I couldn't solve it, but as it turned out I wanted to make users select at least one term from each vocabulary anyway when creating content, so I ignored the problem.

For me there was an access permissions problem particular to Drupal Commons and Hierarchical Select User Terms. I was attempting to use a two-deep taxonomy hierarchy similar to Country->City. I made this a required field during registration. First the user selects Country, then a list of cities becomes available, from which the user selects one. But I was getting "Received an invalid response from the server"‎ error message after the user selected Country.

Apache logs showed the Hierarchical Select field was making a call to server to the Apache server (http://mysite.com/site/hierarchical_select_json). That path was not accessible because I had Site Configuration->Drupal Commons settings set to "Force users to login" and the path "site/hierarchical_select_json" was not specified in "Allowed paths".

Adding "site/hierarchical_select_json" to Allowed paths solved the problem for me.

While I agree that the implementation of the "require users to login" feature isn't ideal, I would expect that being logged in would prevent it from interrupting the Hierarchical Select callback.

Can you clarify why that's not the case?