Hello Andrei,
I was testing the change sets for 1.9version,
In this change set: http://nopcommerce.codeplex.com/SourceControl/changeset/changes/57248
I think 2 changes should be made:
1) textbox mode should be "password" as while typing the topic page password, the password is visible
2) Enter key doesn't work on password protected topic pages, Currently, if we type password and press enter - nothing happens, if have to press enter button manually in order to see page data. But maximum tendency of most of the computer users is that they will press enter rather than pressing the button manually by mouse pointer.