While using the Comments extension on a wikifarm, I notice that there was an issue where a globally blocked IP was leaving comments. This is easily resolved by applying a local block, but it shouldn't be necessary.
Upon investigation, I discovered the extension uses User::isBlocked to decide whether or not to show the reply form. However, User::isBlocked does not report on if the user/IP is currently under a global block. One could use User::isBlockedGlobally in addition to the current check, but the documentation for that function comes with a warning to use something else instead.
Instead, I'd suggest changing the conditional on the line linked above to be:
if ( $this->title->userCan( 'comment', $this->getUser() == false ) && ( $this->allow == '' || $pos !== false ) ) {
I would also recommend similar logic in getVoteLink in Comments.php.
A possible outcome of this change is that it could now be possible to limit the action comment using means other than blocking a user or removing the comment user right (eg by applying comment protection using $wgRestrictionTypes).