Can't reproduce that.
Maybe you'd like to give us a more detailed description. Also: which version, which OS?
Thanks for the reply! I'm on CS6, OSX 10.7.5
Looks like it works when I open the pdf in Acrobat. Apple's "Preview.app" doesn't show the effect if it is placed into a symbol, though. Can you reproduce that?
No, I can't reproduce the Preview issue.
Maybe it is caused by other options in your file.
Anyway: Preview is in no way suitable to pre check files for printing.