From Marvin Theimer, Microsoft:
The main thing I'm after is that the behavior of trying to step "outside" the mountpoint by cd'ing out the top must be 
either (a) prohibited or (b) explicitly marked as undefined in its behavior, with an error fault potentially being 
generated.  This is because in the Windows world I can imagine that a mountpoint definition might map to setting up a 
drive letter and you can't cd up out of a drive letter.

In fact, I'd be happy enough with the profile stating that paths in JSDL documents should not contain either the "." or 
the ".." elements at all. That's a fairly strong requirement and guarantees that the job won't fail on systems where 
your style of semantics are enforced.