Well, I haven't checked for a while (year or two), but it seemed at the time as if Google were blocking Debris. A possible solution is to change your UserAgent string. Something like "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.5) Gecko/20041111 Firefox/1.0" perhaps.
You're only getting one image at a time? Have you checked that your max images is sufficiently high? Or else use like 7 layers. You might want to kill your config and start over. See this thread:
http://forum.cockos.com/showthread.php?p=311269
There is a setting to randomly size images up and down, that could look grainy too.
Let me know if this helps. If you want to post a screenshot to illustrate what you're talking about, I recommend Shup (available at shup.com, support forum is here:
http://forum.cockos.com/forumdisplay.php?f=27