I just bought a Leica X1 which shoots raw in DNG format but the raw DNG files it creates to not display thumbnails in Media Expression (formerly a micorsoft product, now Phase one).
I am running mac OS X 10.6.4
One "solution" offered in the Leica forum was to run the Leica DNG file in DNG converter... I did and it worked but that is a really really clumsy solution to what I feel should not be a problem.... and renaming and deleting original files etc it a real PITA if you shoot any number of photos.
I know that Nikon had issues with new versions of NEF files which had something to do with "header changes" in the NEF file before ACR could decode them, and I'm wondering if there is some similar issue with DNG that I am not aware of.