There is one annoying bug in AutoCAD for Mac (since 2011 initial release), that prevented me from using solid hatches (fills) with transparency in my daily work: if you assign transparency to the solid hatch, on output (to the real plotter/printer or to PDF file) you will get such results:
Recently I accidentally found a kind of workaround for this problem (in order to get right output as you see on the next image):
And here is the solution.
When you create solid fill of some closed area in the drawing, you have to use Gradient with two colors instead of using Hatch with Solid pattern:
Just assign the same color to the “Color 1″ and “Color 2″ in Gradient properties and you will get the expected result when you will print such solid fill with transparency assigned.
As I discovered, when we use Gradient fill with transparency, AutoCAD converts such fill to raster image with opacity during output to PDF (or to the real plot device). This eliminates the side effect (the appearance of the contour lines of the triangles that form the fill).
I have not tested this workaround in AutoCAD 2011 for Mac, but in 2012 and 2013 it works just fine for me. Hope it will help you too.