[mgs]

I haven't read all posts in this topic. Just ignore me if I'm incorrect|this suggestion was already proposed.

From my point of view in the following code

if ($doublepost['userid'] == $vbulletin->userinfo['userid'] AND $doublepost['attach'] == 0)

a little addition should be made

if ($doublepost['userid'] == $vbulletin->userinfo['userid'] AND  $doublepost['parentid'] == $parentid AND $doublepost['attach'] == 0)

This one prevents doubleposting "blank shots" if user answers to the different posts.