Full disclosure: first install of roundcube (0.2alpha); first post to forum; newbie alert! I sincerely hope this is not a brain-dead FAQ, but . . .
I notice that "sometimes" a single clidk on a mail in the listing jumps right to a reply to said message, but without quoting it in the overly hasty reply.
This is, as noted, from the 0.2-alpha tarball. I have the preview pane enabled, and it appears to work ok. Actually, this 'single-click' behaviour is the only thing I can find to complain about!!! Not bad for an alpha!
Best regards,