Commentpress doesn't work for some unauthenticated users

I’m using Commentpress 3.1 (plugin and theme) on WordPress 3.0.1 with multisite enabled.

Sometimes when users are not logged in, when they click on the link to “comment on this paragraph” (or page) it just reloads the page but does not show the comment form. I haven’t figured out what makes this fail or work in different situations, but have reproduced it on several browsers.

Anyone seen this or similar problems before? I’ll take any clues you have, I’m grasping at straws now. Thanks!