Here is the answer you may be looking for:
If we enable Quick Reply, a box will appear on the showthread.php page allowing users to reply to the current thread without needing to load the full newreply.php page.
When Quick Reply is enabled, we may specify whether or not users must click the Quick Reply icon in order to start typing in the Quick Reply editor.
If we choose not to require a click, the system will not know to which post a user is replying, making both the threaded and hybrid display modes nonsensical.
It is strongly recommended that you set the option to require a click if you use Quick Reply and have Threaded Mode available on your forums.
While quick reply is still under pre-load, the...