Sony files imported as DNG into Lightroom 5 have no thumbnails in Finder

I use Lightroom 5 and always convert my RAW files into DNG format when I import photos. Since I converted to OS X the DNG thumbnails from my Sony NEX camera do not show up in Finder. The DNG files coming from my Canon camera do show up as thumbnails. This is a royal pain since you can't see the photos to identify which one you want without opening it up in Lightroom. I have checked with Adobe and they are very clear that this is an Apple problem - which my experience would seem to support since the problem started when I converted to OS X. Any solutions?