Item Lvl 47 Mist Whisper unique same as Item lvl 14 version

The final boss of ACt 3 dropped Mist Whisper crossbow item lvl 47 which i was super excited for, because I have a build that utilizes it. I had this same unique drop early on in the campaign (Act 1 or 2 maybe) and it was awesome. When it dropped off final boss i was disappointed to see the physical damage was the same as the lvl 17 version. 6 - 10 physical and 6- 10 and 6 - 10. All the other stats are pretty much the same. Is this a bug or working as intended? IF tis a bug... PLZ boost my new unique!!! <3