[Plugin: Jetpack by WordPress.com] Comment form not loading when using threaded comments

I’m using WP 3.4.1 and the standard theme Twenty Eleven. When I activate “threaded (nested) comments” in the discussion section, the comment form doesn’t load when I try to reply on a comment. Same behavior with Twenty Eleven.

http://wordpress.org/extend/plugins/jetpack/

[ Please do not bump, that’s not permitted here. ]