Again... it was doing it on xenforo.com(resource manager) when I was posting my updates. I also managed to snag a video of it on Admin Extra which I Believe is running 1.3.0 (Stable release).
Here's a video:
In the start, pasting the copied text on the top line with text works, I then remove it(ctrl-z) hit enter, try pasting again no result, enter paste no result. I then type a few letters, pasting between the letters works... but not on a blank line.
Sure enough I can't replicate right now, but it was doing it last night. Maybe a browser issue.