I just thought I would add here that this is not a bug. Using the sys.path will return the PYTHONPATH, which as Wayne mentioned lists the paths that Python will search for when importing modules. In addition to the PYTHONPATH, Python will also search the PYTHONHOME directory, which is the current working directory of the script being ran.Here is another way to set the workspace to the directory of the script you are running:
import arcpy, os, sys
arcpy.env.workspace = os.path.dirname(sys.argv[0])