So typically when I respond to a post that I want to quote, I use the link in the post to do so. I get redirected to the editor that allows me to type up my post.
Before it completely loads, I place my cursor into the main text box and then press the enter key to drop a line or two below the quote. Doing this sends an enter keystroke to the default action on the page, which is to publish the new post, instead of the textbox. This causes my post to get published without any text other than the quote. I then have to delete the post and try to post again. Only when the page fully loads can I send an enter keystroke to the main textbox.
FWIW, I am running the IE8 beta. Perhaps this is an issue with that rather than the site and/or Invision, but I was curious to see if others were hitting this issue, or if it was just me.