Oh, there's a note about it in the support page:

"Comments containing special ASCII characters (such as the 'hearts' character: ♥) are currently causing problems. Either the 'post comment' button will become grayed out, or you will receive a 'Frank's nibbling on the wires' error; in either case, the comment cannot be posted. Removing these special characters from your comment will allow you to post the comment. This issue is reported."