_pathauto_set_alias fails if there is a newer alias in the url_alias table

After upgrading D6 from an older version (in this case, 6.13 to 6.29), the Automatic alias toggle box on many nodes stopped working. I've tracked it down to the logic in path_set_alias of the path.module. Pathauto.inc is passing the correct source, alias and pid on line 503 of pathauto.inc

path_set_alias($path['source'], $path['alias'], $path['pid'], $path['language']);

However, the query on line 119 of path.module is not checking to see if the existing row that is found has the same alias being sent by pathauto.

$existing = db_fetch_array(db_query("SELECT pid, src FROM {url_alias} WHERE dst = '%s' AND language = '%s' ORDER BY pid DESC", $alias, $language));

In effect, this means that any new aliases that get created from the /admin/build/path interface interfere with pathauto's ability to set the alias, hence the bug.

In my opinion, if core is going to support multiple url aliases to a given path, then the logic should be there to confirm that the alias has changed. That could be something like changing line 120 to:

if (!$existing || $existing['dst'] != $alias || ($existing['pid'] == $pid && $existing['src'] != $path))

However, I'm not familiar enough with paths to know if that's the correct approach. Edit: Upon further reflection, this approach will not work b/c the pid that pathauto is attempting to update is the additional alias, not the one with the correct pathauto dst. I think additional actions will need to be taken within the switch statement that starts on line 474 to delete one of the duplicate aliases.

Thanks for any feedback you can offer.