Photo sync issues

Every time i add new pictures to any of the folders which are used by iTunes to sync photos to my iPhone 6 (IOS8) iTunes deletes all pictures on my phone which were synced and starts copying them again. As with the playlist whenever we add new songs it gets added to the phones playlist. I believe same thing should happen with photos also. Its really annoying weighting for your phone to sync all pics again every time you wanna add new photo to an iPhone. Its happening since i have updated to IOS 8.1.3 and 8.2. I don't know whether its something wrong with IOS or iTunes because with IOS update we get iTunes update also. Please help HOW TO FIX THIS!!?