ArcPy versions are really tied to the underlying ArcGIS for Desktop, Engine, Server, etc... application that is installed. The GetInstallInfo (arcpy) function will let you know which application the currently loaded arcpy package is pointing to along with a bunch of other information, including version.
>>> import arcpy
>>> arcpy.GetInstallInfo()['Version']
u'10.3'
Looking at the ArcGIS 10.3 Issues Addressed List, nothing jumps out at me for CalclateField_management or ArcPy that would seem related to this issue. That said, sometimes bugs get addressed indirectly as the result of a different bug being addressed directly, i.e., not every issue that gets addressed with a new release ends up in the Issues Addressed List.
Looking at your StackExchange post, it appears you are using Enthought Canopy for Python package deployment. I am also wondering if it might be a configuration issue tied to how iPython is being pushed your machine with ArcGIS installed.