It's a border case for backporting. The docs do say it should be returning 
an absolute path, so that is a bug. And chances are anyone who has 
discovered this and is working around it simply called os.path.abspath() 
on the value instead of some manual calculation (if at all; bigger chance 
no one simply noticed).

My vote is to backport. Otherwise the docs should be updated for 2.6/3.1 
to mention the bug.