I noticed that every time I click on "add comment", both my own comment and the comments above get expanded horizontally a bit, so they move partly under the text on the right. Refreshing the page clears the problem, and all comments are displayed correctly again, including my own comment.
I use Firefox on Windows Vista.
I only experience the problem at home, not at work apparently. At home it's Windows Vista. I'll take a screenshot tonight.
EDIT : screenshot :