I am experiencing the same issue.
The disk is new and was initialized as GPT, but even so shows up as 1678GB
I set up an identical drive 2 weeks ago at 4TB
The only difference is the system they were initialized on. The drive that was set up 2 weeks ago was on Win 8 in an external USB bay. The new drive was initialized on server 2012 on SATA.
A) Even inside the DISKPART utility, and after moving the new drive to the external USB bay on the WIn 8 system, it shows up at 1678GB. I also did a CLEAN on it and no change.
B) The drive that was successfully formatted to 4TB shows up at 1.64TB in the disk manager on Server 2012, even though it contains a 3.64TB partition.