This is a new "feature" that I didn't experience in LR5 or previous when importing my CR2 RAW files into DNG. Now with LR6 CC, I occasionally find from 3 to 15 or so CR2 files in the folder along with the DNGs. All the DNGs are there, but the CR2s are not always being removed after conversion. Seems to happen about 60-70% of the time. No error messages. I think this new 2-step import/conversion is not working completely right.
Windows 8.1 x64
All Lightroom Library folders/images are located on a server drive array with hardware RAID5.
Imports/DNG Conversions are typically sets of around 4GB (200 or so images) of RAW files from Canon 5dMKIII