Ugh, Rob, that's ugly. One more inheritance from aD, I'm afraid, that no one here bothered to track down. I've never tried ecommerce installed in a novel directory, but clearly if you're allowed to parameterize its home, it should work. Grrrr....
Fortunately for 4.x we have more experience with aD code and a larger volunteer hacker base than we ever did for 3.x. This is a lesson all 4.x volunteers should learn - let's be sure we test as many combinations of package parameters as we possibly can.