User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:188.8.131.52) Gecko/20071203 IceWeasel/184.108.40.206 (Zenwalk GNU Linux)
Open the notification settings, and click preview. Now, close the preview notification. The show preview button is disabled, so you can't re-show the preview notification without closing and re-opening the settings window first.
Also, the notification preview doesn't update its position to reflect the current selection. It has to be reshown using the method above.
xfce4-notifyd has no preview button.
Are you talking about notification-daemon-xfce? If so, it's unmaintained; you should be using xfce4-notifyd if you want something maintained and actively developed.
I'm not sure about OP but I has this problem in notification-daemon-xfce. I'll move to newer notification daemon. Thanks.