comment with empty title doesn't get a title automatically set anymore

Problem is that comment_validate is doing the subject insertion, but comment_form_validate just loses all those changes. _validate doesn't seem like the right place to be making adjustments and I don't think that the forms api supports that anyway.

I tried it out -- modifiying comment_form_validate to pass its arguments by reference still ends up with the subject getting lost before _execute is called.

So the solution seems to be to move that comment munging code from _validate to _execute.

Attaching a patch which moves the subject-adding snippet of code to comment_form_execute and renames $edit to $form_values in that snippet to correspond to the new scope.

From a cursory look at the code in the patch in http://drupal.org/node/35726#comment-56632
it looks like you're handling the preview case as well, which I don't remember caring about when making this patch.