How you are you creating the PDF? File | Print or toolbar button?
Adobe has been doing quite a bit of work in getting direct (first-person) access to the XPS subsystem so that PDF creation can be faster and of higher quality than ramming the PostScript camel through the eye of a needle (File | Print).
I would also take a look under the 'advanced' button in File | Print. Make sure you are using the Adobe Default print settings - at least as a starting point. That such nefarious items as print as image, and image conversion settings are not enabled.
Hope this helps.