iTunes doesn't sync IPTC keywords within .DNG files to iPhone

After much testing it appears that iTunes 12.1.2.27 (Windows) will sync both .JPG images and .DNG (digital negative) images to the iPhone. They can both be viewed and used normally. In addition, IPTC keywords that are added to a .JPG file IPTC header on the computer (perhaps with Lightroom or Picasa) will be updated on the iPhone during the next sync session using iTunes. The keywords can then be seen using any number of iPhone apps.

However, if updates are made to a .DNG file on the computer with Lightroom or Picasa, the files are updated on the computer but even when synced using iTunes manually, the keywords do not appear to be included. In fact, no keyword data from a .DNG file can be seen on the iPhone with metadata viewers even if the keywords existed before the initial sync.

Can anyone else confirm this?.

Since the current photos app on iPhone (iOS 8.3) doesn't have a method to display or search by IPTC data (a serious oversight), it would be nice to at least have the iTunes sync process work properly to enable keyword searches using other apps like Smart Album by NexTiga.