I have two hard drives in my MacBook Pro: one is a solid state drive that holds the OS and Applications, the other a spinning platter drive that holds my home directory.
I currently have /Users/ian as a symlink to /Volumes/Macintosh HD/Users/ian.
And in my user profile my home directory is /Users/ian:

When I change the Home directory field to /Volumes/Macintosh HD/Users/ian and perform the requested restart of my machine, after I log back in, my home directory is set back to /Users/ian.
Why won't my changes to this setting stick?