problem with clipping in inkscape (despite it usually working...)

I'm still pretty new at inkscape, but I've learned how to clip...with no problem up until now.

I've made a circle with a design in it (made out of grouped objects) and a peace sign (also made out of grouped objects) that's the same size as the circle. What I'm trying to do is make the circle into a peace sign shape by placing the peace sign over the circle and using the clip function (object -> clip -> set). Every time I do this, the peace sign disappears and I'm left with the original circle (not a clipped version of the circle).

I've tried things like changing layering, copying the objects into a new file, etc., but nothing's working. Btw, if I use the mask function, it works no problem (I get a peace sign shaped circle) - but I don't want a faded out version of the circle, I want the original version.

Any suggestions?

Thanks very much for any help or ideas you might be able to provide.