We have password protected forums for individual customer organizations. They post support questions and wait for someone to reply. When they get the reply notification in their email, they click the link, are prompted for a password, but are never taken to the post itself.
It seems that the process of providing the password is not retaining the requested post information.
This isn't a problem for administrators as they are never prompted for forum passwords, and the link takes them right into the post. It only affects regular users.
Create a non-administrative user.
Create a password protected forum.
Create a post as the non-administrative user in the password protected forum with reply notification on.
Reply to the post as another user.
Click on the link that is sent to the non-administrative user and proceed as normal (enter password, etc.)