If I have a bug page open for a while, during which my session lapses, then attempt to edit the bug (adding a lengthy comment), I am redirected to a login page, and thence a list of my open bugs. If I move back to the bug page in my browser history, the comment has been replaced with <p></p>.
This happens on Ubuntu/Chromium 18.0.1025.168 and Ubuntu/Firefox 13.0.1. I haven't (yet) experienced it on other machines, though this is the main one I use for development.
