I've open the following bug on launchpad for this issue:
A non-hidden default source tree
https://bugs.launchpad.net/asdf/+bug/1293278
—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org
A programming language is low level
when its programs require attention to the irrelevant.
— Alan Perlis