I probably do it wrong too, but I press the quote button if I want all the post or if I only want say one line, I highlight then copy and paste it, then highlight and press quote again.The only difference is you have to put the senders name in yourself.
If I am adding several different lines, from subjects with several pages,I open the site twice and leave one of them at the bottom of my screen.You can then go back and to without loosing your reply.
If I am writing a long post I regularly copy and paste as a find the site as a habit of going haywire midstream. This way you can retrieve most of what you have written.