Opacity of popup windows affects xscreensaver window

[Qiangning Hong]

I like the function to set opacity of popup windows in Xfce 4.3.90.1
very much.  However, when I set it to some transparent, the xscreensaver
window is transparent too. Even after it blanks out, my desktop is
shown.  It's not good for privacy and healthy of my LCD.  Can let
xscreensaver be an exception of popup windows?

-- 
Qiangning Hong
http://www.hongqn.com