The issue has to do with the font and the way that photoshop is making the fill for the letters.
One solution is to flatten the layers. This will change the way the fill is made and will get rid of the issue, however, it makes all the type raster which is a slight downside.
The other way is to modify the fill in the PDF after it is created. This keeps the type vector. Since the type is vector it will allow for higher quality print. (We recommend using this fix)