Masks not being preserved through printing

Hello,

I created a logo in Illustrator (CS6), then used a mask to cover parts of it.

Next, I placed the logo into the flyer on InDesign.

Everything works fine until I export it to a PDF, where the part that is masked shows up as opaque.

I checked in Acrobat -- the mask is preserved on there. My concern, however, is that I want to publish the flyer digitally as well. I have looked all over online but can't quite find a solution to this problem. Any help that you can give would be greatly appreciated!