What version are you running?
2.0.x-2.5.x
What's the URL of the page containing the problem?
/r/id/diff/
What steps will reproduce the problem?

Click a line and enter some text for the comment, but don't save.
Click another line to create a new comment.

What is the expected output? What do you see instead?
The page should warn when you're about to create a new comment and lose the old one. Instead, it silently closes the old dialog and creates a new one, losing the old comment.
What operating system are you using? What browser?
Any browser.