[Inkscape-user] pattern not into pdf

hello all

I was just finishing another cave map. It is a sandstone cave, so there is a lot of sand on the ground, which is represented by small dots (circles). I created a pattern from some circles to represent the sand, and applied it to a large polygon area. fine. now I export it to a pdf and the pattern is gone! So I tried to convert the pattern to an object, in the hope that this would create lots of small circles where they where in the pattern, but it just made the original set of circles again.. Of course, creating a few thousand points manually is out of question, so how can I have the pattern in my pdfs? or how to convert the pattern to a lot of indivisual objects? thanks Carlos