To elaborate on twbird:
You're hitting the "quote" button (little talk bubble) inside the reply box and cutting and pasting in the quote you want.
We're hitting the button that says "quote" right above their post, which launches into a reply with the quote embedded, and then deleting the stuff we DON'T want to quote.
Also you can, while in the reply box, scroll down and click "Insert Quote" and it will add in their full post and you can remove what you don't want to quote.