Must confess I wasn't aware of that, but bear in mind that will quote the whole of their post. If you want to quote only a selection you will have to amend the resulting copy.
Alternatively, you can select and copy (Ctrl-C) the part of the post you want to quote, click on the Quote button in the menu that appears when you click Reply (the last one on the right that looks like a page of writing) place the cursor between the brackets and paste (Ctrl-V).
That doesn't read as simply as it should, but try it, it is easy.