I think it is just caused by a bit of confusion. When you hit Reply to member" the quoted bit fills the message box, and right underneath, showing no space for you to type your actual response unless you know to scroll down, you see the bright blue "post reply" button - so I think people are automatically hitting that, and then typing their actual response in the blank reply box that they can then see. If you follow me! Because there, it says "write your reply".Where 'this' is subsequent post.
Yes but maybe more members are posting.
The post containing only the quote is often followed by a post from the same member who could have edited the first post and added their message.
What facility are you testing?