Same problem here. Enable the comments feature in JetPack 1.4.2 with WordPress 3.4.1 using the Suffusion theme and when you confirm the comment you get a 403 Forbidden error in wp-comments-post.php
Disable the feature (Learn More button in JetPack feature page, Deactivate button) and comments begin working again. No need to disable the plugin, just this (comment) specific feature.
Edit: It’s like Brownstone73 says, above. The new “Post Comment” button links to https://jetpack.wordpress.com/jetpack-comment/ which is not quite what I expected. Either way, that’s a broken link.
The old “Submit Comment” button (with the JetPack comment feature disabled) links to where you’d expect …your wp url…/wp-comments-post.php
So, don’t know what’s going on here. Can’t find anywhere to configure the comment link …
