From https://answers.atlassian.com/questions/489/how-do-we-provide-code-blocks-in-these-questions:

I am not sure this code block feature is working as intended across browsers.

I do see that we now have a live preview option, which has been helpful while forming this comment to demonstrate what I see happening here

For what it's worth, I started trying to enter this comment via Safari v5.1 - and the comment button does not seem to work in Safari. The cancel button does, but comment simply does nothing.