You can just press the 'quote' tab, to the right of the 'reply' tab on the post that you want to quote.
Then it will quote that persons post and you can answer under it.
It works for me that way but it's the same when using speech bubbles so I don't know what you are doing wrong.
What you can do however, is using the 'go advanced' mode instead of the 'quick reply' mode.
This way, you can check out how your post is going to look like before posting it, so you can screw around with the quote thing until you figure it out

If you are still having problems after this, then there is a support forum where you can ask further questions regarding this matter, just in case you don't get your question answered in this thread.
Support forum:
http://www.bluelight.org/vb/forums/111-Support