I have used Lightroom for years and have always converted RAW files upon import to DNG with upper case file extension. After upgrading to LR CC, however, all of my files are imported and converted to DNG with the lower case .dng extension. Preferences in Edit and Import are still checked to upper case. I still have LR 5.7 installed on my system and it still correctly uses the upper case .DNG file extension, so this is apparently another bug with LR CC. Not a serious issue, but annoying nonetheless.