Bug in farmconfig.py or user error?

I'll admit I'm not much of a Python programmer. I'm not sure if the following is a bug or an error on my part...
Setting data_underlay_dir in farmconfig.py has no effect on my system.  farmconfig.py *is* getting executed (I added debugging print
statements). When I set data_underlay_dir in farmconfig.py, I still get the default value.  Setting it in wikiconfig.py works.
Printing it in farmconfig before I set it does not print the value from the default class -- it produces an error.
 
Is it a bug, or am I just confused about how subclassing works in Python?
 
Kevin Kleinfelter
Programming Manager, Atlanta  / IT Lead, Wells Fargo Projects
Regulus Group, LLC
770-806-2476